gitk: Pass --invert-grep option down to "git log"

"git log --grep=<string>" shows only commits with messages that
match the given string, but sometimes it is useful to be able to
show only commits that do *not* have certain messages (e.g. "show
me ones that are not FIXUP commits").

Now the underlying "git log" learned the "--invert-grep" option.
The option syntactically behaves similar to "--all-match" that
requires that all of the grep strings to match and semantically
behaves the opposite---it requires that none of the grep strings to
match.

Teach "gitk" to allow users to pass it down to underlying "git log"
command by adding it to the known_view_options array.

Signed-off-by: Christoph Junghans <ottxor@gentoo.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

gitk

@@ -4066,6 +4066,7 @@ set known_view_options {
     {committer t15  .  "--committer=*"  {mc "Committer:"}}
     {loginfo   t15  .. "--grep=*"       {mc "Commit Message:"}}
     {allmatch  b    .. "--all-match"    {mc "Matches all Commit Info criteria"}}
+    {igrep     b    .. "--invert-grep"  {mc "Matches none Commit Info criteria"}}
     {changes_l l    +  {}               {mc "Changes to Files:"}}
     {pickaxe_s r0   .  {}               {mc "Fixed String"}}
     {pickaxe_t r1   .  "--pickaxe-regex"  {mc "Regular Expression"}}