Allow INSTALL, bindir, mandir to be set in main Makefile

Makefiles in subdirectories now use existing value of INSTALL, bindir,
mandir if it is set, allowing those to be set in main Makefile or in
included config.mak.  Main Makefile exports variables which it sets.

Accidentally it renames bin to bindir in Documentation/Makefile
(should be bindir from start, but is unused, perhaps to be removed).

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/Makefile

@@ -25,8 +25,8 @@ DOC_MAN1=$(patsubst %.txt,%.1,$(MAN1_TXT))
 DOC_MAN7=$(patsubst %.txt,%.7,$(MAN7_TXT))
 
 prefix?=$(HOME)
-bin=$(prefix)/bin
-mandir=$(prefix)/man
+bindir?=$(prefix)/bin
+mandir?=$(prefix)/man
 man1=$(mandir)/man1
 man7=$(mandir)/man7
 # DESTDIR=

Makefile

@@ -100,6 +100,8 @@ template_dir = $(prefix)/share/git-core/templates/
 GIT_PYTHON_DIR = $(prefix)/share/git-core/python
 # DESTDIR=
 
+export prefix bindir gitexecdir template_dir GIT_PYTHON_DIR
+
 CC = gcc
 AR = ar
 TAR = tar

contrib/emacs/Makefile

@@ -3,9 +3,9 @@
 EMACS = emacs
 
 ELC = git.elc vc-git.elc
-INSTALL = install
+INSTALL ?= install
 INSTALL_ELC = $(INSTALL) -m 644
-prefix = $(HOME)
+prefix ?= $(HOME)
 emacsdir = $(prefix)/share/emacs/site-lisp
 
 all: $(ELC)

contrib/git-svn/Makefile

@@ -1,8 +1,8 @@
 all: git-svn
 
 prefix?=$(HOME)
-bindir=$(prefix)/bin
-mandir=$(prefix)/man
+bindir?=$(prefix)/bin
+mandir?=$(prefix)/man
 man1=$(mandir)/man1
 INSTALL?=install
 doc_conf=../../Documentation/asciidoc.conf