[jhbuild] add source code comment about the previous change

[Frederic Peters <fpeters src gnome org>]

commit 95bb0e0b01ed83d982212851a50e53958bc7a44e
Author: Frédéric Péters <fpeters 0d be>
Date:   Sat May 23 17:13:32 2009 +0200

    add source code comment about the previous change
---
 Makefile.plain |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/Makefile.plain b/Makefile.plain
index 43310b5..6f8185d 100644
--- a/Makefile.plain
+++ b/Makefile.plain
@@ -37,6 +37,9 @@ install: install-check
 	@[ -f $(HOME)/.jhbuildrc ]||echo "Don't forget to create ~/.jhbuildrc"
 	install -m755 install-check $(bindir)/install-check
 
+	# if ~/bin/jbuild exists, it is most likely an old version, and it will
+	# not work; so rename it and install a symlink to the new version
+	# instead.
 	@if [ -e "$(HOME)/bin/jhbuild" ] && [ ! $(bindir) -ef $(HOME)/bin ]; then \
 		mv "$(HOME)/bin/jhbuild" "$(HOME)/bin/jhbuild.old" ; \
 		ln -s $(bindir)/jhbuild "$(HOME)/bin/jhbuild" ; \