check-docs: fix for setups where executables have an extension

On Windows, for example, executables (must) have the extension `.exe`.
Our `check-docs` target was not prepared for that.

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

Makefile

@@ -3057,7 +3057,7 @@ ALL_COMMANDS += git-gui git-citool
 .PHONY: check-docs
 check-docs::
 	$(MAKE) -C Documentation lint-docs
-	@(for v in $(ALL_COMMANDS); \
+	@(for v in $(patsubst %$X,%,$(ALL_COMMANDS)); \
 	do \
 		case "$$v" in \
 		git-merge-octopus | git-merge-ours | git-merge-recursive | \
@@ -3087,7 +3087,7 @@ check-docs::
 		    -e 's/\.txt//'; \
 	) | while read how cmd; \
 	do \
-		case " $(ALL_COMMANDS) " in \
+		case " $(patsubst %$X,%,$(ALL_COMMANDS)) " in \
 		*" $$cmd "*)	;; \
 		*) echo "removed but $$how: $$cmd" ;; \
 		esac; \