vis/unvis: pull in exact implementation from FreeBSD

Perhaps this is not completely ideal, because it brings in cgo.
And with the flags, it can have tailored experience.

I've added a basic test to ensure that the cases we're interested in are
covered.

This does not yet integrate the usage of Vis()/Unviz() into the manifest
create and compare.

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

vis.h

@@ -0,0 +1,90 @@
+/*-
+ * Copyright (c) 1990, 1993
+ *      The Regents of the University of California.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. All advertising materials mentioning features or use of this software
+ *    must display the following acknowledgement:
+ *      This product includes software developed by the University of
+ *      California, Berkeley and its contributors.
+ * 4. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ *      @(#)vis.h       8.1 (Berkeley) 6/2/93
+ * $FreeBSD$
+ */
+
+#ifndef _VIS_H_
+#define _VIS_H_
+
+#include <sys/types.h>
+
+/*
+ * to select alternate encoding format
+ */
+#define VIS_OCTAL       0x01    /* use octal \ddd format */
+#define VIS_CSTYLE      0x02    /* use \[nrft0..] where appropriate */
+
+/*
+ * to alter set of characters encoded (default is to encode all
+ * non-graphic except space, tab, and newline).
+ */
+#define VIS_SP          0x04    /* also encode space */
+#define VIS_TAB         0x08    /* also encode tab */
+#define VIS_NL          0x10    /* also encode newline */
+#define VIS_WHITE       (VIS_SP | VIS_TAB | VIS_NL)
+#define VIS_SAFE        0x20    /* only encode "unsafe" characters */
+
+/*
+ * other
+ */
+#define VIS_NOSLASH     0x40    /* inhibit printing '\' */
+#define VIS_HTTPSTYLE   0x80    /* http-style escape % HEX HEX */
+#define VIS_GLOB        0x100   /* encode glob(3) magics */
+
+/*
+ * unvis return codes
+ */
+#define UNVIS_VALID      1      /* character valid */
+#define UNVIS_VALIDPUSH  2      /* character valid, push back passed char */
+#define UNVIS_NOCHAR     3      /* valid sequence, no character produced */
+#define UNVIS_SYNBAD    -1      /* unrecognized escape sequence */
+#define UNVIS_ERROR     -2      /* decoder in unknown state (unrecoverable) */
+
+/*
+ * unvis flags
+ */
+#define UNVIS_END       1       /* no more characters */
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+char    *vis(char *, int, int, int);
+int     strvis(char *, const char *, int);
+int     strvisx(char *, const char *, size_t, int);
+int     strunvis(char *, const char *);
+int     strunvisx(char *, const char *, int);
+int     unvis(char *, int, int *, int);
+__END_DECLS
+
+#endif /* !_VIS_H_ */