Add tag matching to input attributes.

Tags may be a list of comma-separated strings that match against a MatchTag
InputClass section. If any of the tags specified for a device match against
the MatchTag of the section, this match is evaluated true and passed on to
the next match condition.

Tags are specified as "input.tags" (hal) or "ID_INPUT.tags" (udev), the
value of the tags is case-sensitive and require an exact match (not a
substring match).

i.e. "quirk" will not match "QUIRK", "need_quirk" or "quirk_needed".

Example configuration:
udev:
    ENV{ID_INPUT.tags}="foo,bar"

hal:
    <merge key="input.tags" type="string">foo,bar</merge>

xorg.conf:
    Section "InputClass"
            Identifier "foobar quirks"
            MatchTag "foo|foobar"
            Option "Foobar" "on"
    EndSection

Where the xorg.conf section matches against any device with the tag "foo"
or tag "foobar" set.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Tested-by: Dan Nicholson <dbn.lists@gmail.com>
Reviewed-by: Dan Nicholson <dbn.lists@gmail.com>

hw/xfree86/doc/man/xorg.conf.man.pre

@@ -1054,6 +1054,15 @@ This entry can be used to check if the device file matches the
 pathname pattern. Multiple patterns can be matched by separating arguments
 with a '|' character.
 .TP 7
+.BI "MatchTag \*q" matchtag \*q
+This entry can be used to check if tags assigned by the config backend
+matches the
+.RI \*q matchtag \*q
+pattern.  Multiple patterns can be matched by separating arguments
+with a '|' character. A match is found if at least one of the tags given in
+.RI \*q matchtag \*q
+matches at least one of the tags assigned by the backend.
+.TP 7
 .BI "MatchIsKeyboard     \*q" bool \*q
 .TP 7
 .BI "MatchIsPointer      \*q" bool \*q