git-p4: Allow setting rename/copy detection threshold

Copy and rename detection arguments (-C and -M) allow setting a threshold value
for the similarity ratio. If the similarity is below this threshold the rename
or copy is ignored and the file is added as new.
This patch allows setting git-p4.detectRenames and git-p4.detectCopies options
to an integer value to set the respective threshold.

Signed-off-by: Vitor Antunes <vitor.hda@gmail.com>
Acked-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/fast-import/git-p4

@@ -774,15 +774,20 @@ class P4Submit(Command, P4UserMap):
 
         if not self.detectRenames:
             # If not explicitly set check the config variable
-            self.detectRenames = gitConfig("git-p4.detectRenames").lower() == "true"
+            self.detectRenames = gitConfig("git-p4.detectRenames")
 
-        if self.detectRenames:
+        if self.detectRenames.lower() == "false" or self.detectRenames == "":
+            diffOpts = ""
+        elif self.detectRenames.lower() == "true":
             diffOpts = "-M"
         else:
-            diffOpts = ""
+            diffOpts = "-M%s" % self.detectRenames
 
-        if gitConfig("git-p4.detectCopies").lower() == "true":
+        detectCopies = gitConfig("git-p4.detectCopies")
+        if detectCopies.lower() == "true":
             diffOpts += " -C"
+        elif detectCopies != "" and detectCopies.lower() != "false":
+            diffOpts += " -C%s" % detectCopies
 
         if gitConfig("git-p4.detectCopiesHarder").lower() == "true":
             diffOpts += " --find-copies-harder"