Support reading the tag message from a file in release/hotfix finish

This option ('-f' because '-F' was already taken) maps to the 'tag -F' option, and avoids the
problem with issue nvie#98 (nvie#98) on Mac

git-flow-hotfix

@@ -221,6 +221,7 @@ cmd_finish() {
 	DEFINE_boolean sign false "sign the release tag cryptographically" s
 	DEFINE_string signingkey "" "use the given GPG-key for the digital signature (implies -s)" u
 	DEFINE_string message "" "use the given tag message" m
+	DEFINE_string messagefile "" "use the contents of the given file as tag message" f
 	DEFINE_boolean push false "push to $ORIGIN after performing finish" p
 	DEFINE_boolean keep false "keep branch after performing finish" k
 	DEFINE_boolean notag false "don't tag this release" n
@@ -269,6 +270,7 @@ cmd_finish() {
 			flag sign && opts="$opts -s"
 			[ "$FLAGS_signingkey" != "" ] && opts="$opts -u '$FLAGS_signingkey'"
 			[ "$FLAGS_message" != "" ] && opts="$opts -m '$FLAGS_message'"
+			[ "$FLAGS_messagefile" != "" ] && opts="$opts -F '$FLAGS_messagefile'"
 			eval git tag $opts "$VERSION_PREFIX$VERSION" || \
 			die "Tagging failed. Please run finish again to retry."
 		fi

git-flow-release

@@ -190,6 +190,7 @@ cmd_finish() {
 	DEFINE_boolean sign false "sign the release tag cryptographically" s
 	DEFINE_string signingkey "" "use the given GPG-key for the digital signature (implies -s)" u
 	DEFINE_string message "" "use the given tag message" m
+	DEFINE_string messagefile "" "use the contents of the given file as a tag message" f
 	DEFINE_boolean push false "push to $ORIGIN after performing finish" p
 	DEFINE_boolean keep false "keep branch after performing finish" k
 	DEFINE_boolean notag false "don't tag this release" n
@@ -239,6 +240,7 @@ cmd_finish() {
 			flag sign && opts="$opts -s"
 			[ "$FLAGS_signingkey" != "" ] && opts="$opts -u '$FLAGS_signingkey'"
 			[ "$FLAGS_message" != "" ] && opts="$opts -m '$FLAGS_message'"
+			[ "$FLAGS_messagefile" != "" ] && opts="$opts -F '$FLAGS_messagefile'"
 			eval git tag $opts "$tagname" || \
 			die "Tagging failed. Please run finish again to retry."
 		fi