help -a: do not list commands that are excluded from the build

When built with NO_CURL or with NO_UNIX_SOCKETS, some commands are
skipped from the build. It does not make sense to list them in the
output of `git help -a`, so let's just not.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

generate-cmdlist.sh

@@ -6,7 +6,7 @@ die () {
 }
 
 command_list () {
-	grep -v '^#' "$1"
+	eval "grep -ve '^#' $exclude_programs" <"$1"
 }
 
 get_categories () {
@@ -93,6 +93,14 @@ EOF
 EOF
 }
 
+exclude_programs=
+while test "--exclude-program" = "$1"
+do
+	shift
+	exclude_programs="$exclude_programs -e \"^$1 \""
+	shift
+done
+
 echo "/* Automatically generated by generate-cmdlist.sh */
 struct cmdname_help {
 	const char *name;