* progmodes/grep.el (grep-regexp-alist): Use more-accurate regexp.

* progmodes/grep.el (grep-regexp-alist): Use more-accurate regexp.

Do not match file names that end in '/', as they cannot be 'grep'
hits nowadays.  This prevents confusion when 'grep -r' reports a
match in a file whose basename is ':12345:'.  Conversely, do not
require exactly the same sequence of spaces and tabs after both
colons, and allow spaces or tabs before the second colon, as per
the POSIX spec for 'grep' output.