Move gitk to its own subdirectory

This is to prepare for gitk i18n effort that makes gitk not a single file
project anymore.  We may use subproject to bind git.git and gitk.git more
loosely in the future, but we do not want to require everybody to have
subproject aware git to be able to pull from git.git yet.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

gitk-git/Makefile

@@ -0,0 +1,29 @@
+# The default target of this Makefile is...
+all::
+
+prefix ?= $(HOME)
+bindir ?= $(prefix)/bin
+TCLTK_PATH ?= wish
+INSTALL ?= install
+RM ?= rm -f
+
+DESTDIR_SQ = $(subst ','\'',$(DESTDIR))
+bindir_SQ = $(subst ','\'',$(bindir))
+TCLTK_PATH_SQ = $(subst ','\'',$(TCLTK_PATH))
+
+ifndef V
+	QUIET          = @
+	QUIET_GEN      = $(QUIET)echo '   ' GEN $@ &&
+endif
+
+all:: gitk-wish
+install:: all
+	$(INSTALL) gitk-wish '$(DESTDIR_SQ)$(bindir_SQ)'/gitk
+clean::
+	$(RM) gitk-wish
+
+gitk-wish: gitk
+	$(QUIET_GEN)$(RM) $@ $@+ && \
+	sed -e '1,3s|^exec .* "$$0"|exec $(subst |,'\|',$(TCLTK_PATH_SQ)) "$$0"|' <gitk >$@+ && \
+	chmod +x $@+ && \
+	mv -f $@+ $@