Lint on pkg/* packages

- pkg/useragent
- pkg/units
- pkg/ulimit
- pkg/truncindex
- pkg/timeoutconn
- pkg/term
- pkg/tarsum
- pkg/tailfile
- pkg/systemd
- pkg/stringutils
- pkg/stringid
- pkg/streamformatter
- pkg/sockets
- pkg/signal
- pkg/proxy
- pkg/progressreader
- pkg/pools
- pkg/plugins
- pkg/pidfile
- pkg/parsers
- pkg/parsers/filters
- pkg/parsers/kernel
- pkg/parsers/operatingsystem

Signed-off-by: Vincent Demeester <vincent@sbr.pm>

tailfile/tailfile.go

@@ -1,3 +1,5 @@
+// Package tailfile provides helper functinos to read the nth lines of any
+// ReadSeeker.
 package tailfile
 
 import (
@@ -10,9 +12,11 @@ import (
 const blockSize = 1024
 
 var eol = []byte("\n")
-var ErrNonPositiveLinesNumber = errors.New("Lines number must be positive")
 
-//TailFile returns last n lines of file f
+// ErrNonPositiveLinesNumber is an error returned if the lines number was negative.
+var ErrNonPositiveLinesNumber = errors.New("The number of lines to extract from the file must be positive")
+
+//TailFile returns last n lines of reader f (could be a fil).
 func TailFile(f io.ReadSeeker, n int) ([][]byte, error) {
 	if n <= 0 {
 		return nil, ErrNonPositiveLinesNumber