path.Match works purely with strings, not file paths. That's what sets
it apart from filepath.Match. For example, only filepath.Match will
change its behavior towards backslashes on Windows, to accomodate for
the file path separator on that system.

As such, path.Match should make no mention of file names. Nor should
path.ErrBadPattern mention globbing at all - the package has no notion
of globbing, and the error concerns only patterns.

For a similar reason, remove the mention of globbing from
filepath.ErrBadPattern. The error isn't reserved to just globbing, as it
can be returned from filepath.Match. And, as before, it only concerns
the patterns themselves.

Change-Id: I58a83ffa3e2549625d8e546ef916652525504bd1
Reviewed-on: https://go-review.googlesource.com/87857Reviewed-by: Rob Pike <r@golang.org>