mergetool--lib: add p4merge as a pre-configured mergetool option

Add p4merge to the set of built-in diff/merge tools, and update
bash completion and documentation.

Signed-off-by: Scott Chacon <schacon@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/git-difftool.txt b/Documentation/git-difftool.txt
index 96a6c51..8e9aed6 100644
--- a/Documentation/git-difftool.txt
+++ b/Documentation/git-difftool.txt
@@ -31,7 +31,7 @@
 	Use the diff tool specified by <tool>.
 	Valid merge tools are:
 	kdiff3, kompare, tkdiff, meld, xxdiff, emerge, vimdiff, gvimdiff,
-	ecmerge, diffuse, opendiff and araxis.
+	ecmerge, diffuse, opendiff, p4merge and araxis.
 +
 If a diff tool is not specified, 'git-difftool'
 will use the configuration variable `diff.tool`.  If the
diff --git a/Documentation/git-mergetool.txt b/Documentation/git-mergetool.txt
index 68ed6c0..4a6f7f3 100644
--- a/Documentation/git-mergetool.txt
+++ b/Documentation/git-mergetool.txt
@@ -27,7 +27,7 @@
 	Use the merge resolution program specified by <tool>.
 	Valid merge tools are:
 	kdiff3, tkdiff, meld, xxdiff, emerge, vimdiff, gvimdiff, ecmerge,
-	diffuse, tortoisemerge, opendiff and araxis.
+	diffuse, tortoisemerge, opendiff, p4merge and araxis.
 +
 If a merge resolution program is not specified, 'git-mergetool'
 will use the configuration variable `merge.tool`.  If the
diff --git a/Documentation/merge-config.txt b/Documentation/merge-config.txt
index c0f96e7..a403155 100644
--- a/Documentation/merge-config.txt
+++ b/Documentation/merge-config.txt
@@ -23,7 +23,7 @@
 	Controls which merge resolution program is used by
 	linkgit:git-mergetool[1].  Valid built-in values are: "kdiff3",
 	"tkdiff", "meld", "xxdiff", "emerge", "vimdiff", "gvimdiff",
-	"diffuse", "ecmerge", "tortoisemerge", "araxis", and
+	"diffuse", "ecmerge", "tortoisemerge", "p4merge", "araxis" and
 	"opendiff".  Any other value is treated is custom merge tool
 	and there must be a corresponding mergetool.<tool>.cmd option.
 
diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index e3ddecc..2a9a889 100755
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -953,7 +953,7 @@
 }
 
 __git_mergetools_common="diffuse ecmerge emerge kdiff3 meld opendiff
-			tkdiff vimdiff gvimdiff xxdiff araxis
+			tkdiff vimdiff gvimdiff xxdiff araxis p4merge
 "
 
 _git_difftool ()
diff --git a/git-mergetool--lib.sh b/git-mergetool--lib.sh
index bfb01f7..f7c571e 100644
--- a/git-mergetool--lib.sh
+++ b/git-mergetool--lib.sh
@@ -46,7 +46,7 @@
 valid_tool () {
 	case "$1" in
 	kdiff3 | tkdiff | xxdiff | meld | opendiff | \
-	emerge | vimdiff | gvimdiff | ecmerge | diffuse | araxis)
+	emerge | vimdiff | gvimdiff | ecmerge | diffuse | araxis | p4merge)
 		;; # happy
 	tortoisemerge)
 		if ! merge_mode; then
@@ -130,6 +130,19 @@
 			"$merge_tool_path" "$LOCAL" "$REMOTE"
 		fi
 		;;
+	p4merge)
+		if merge_mode; then
+		    touch "$BACKUP"
+			if $base_present; then
+				"$merge_tool_path" "$BASE" "$LOCAL" "$REMOTE" "$MERGED"
+			else
+				"$merge_tool_path" "$LOCAL" "$LOCAL" "$REMOTE" "$MERGED"
+			fi
+			check_unchanged
+		else
+			"$merge_tool_path" "$LOCAL" "$REMOTE"
+		fi
+		;;
 	meld)
 		if merge_mode; then
 			touch "$BACKUP"
@@ -323,7 +336,7 @@
 		else
 			tools="opendiff kdiff3 tkdiff xxdiff meld $tools"
 		fi
-		tools="$tools gvimdiff diffuse ecmerge araxis"
+		tools="$tools gvimdiff diffuse ecmerge p4merge araxis"
 	fi
 	if echo "${VISUAL:-$EDITOR}" | grep emacs > /dev/null 2>&1; then
 		# $EDITOR is emacs so add emerge as a candidate