Dynamically collect the true git exec path and only if that can not be found,...

Dynamically collect the true git exec path and only if that can not be found, use the default. Variable GIT_EXEC_PATH remains overwritable explicitly when given as a command to 'make'.

Makefile

-GIT_EXEC_PATH=/usr/libexec/git-core
+GIT_EXEC_PATH=`git --exec-path 2>/dev/null || echo /usr/libexec/git-core`
 
 all:
 	@echo "There is only one target here: install"

README.mdown

@@ -24,13 +24,18 @@ To install `git-flow` as a real `git` subcommand, run:
 
 	$ sudo make install
 
-By default, this will install `git-flow` into the default Git exec path
-(`/usr/libexec/git-core`). To override this setting in case you have installed
-Git in another location, use:
+By default, this will look for the directory where Git is already installed,
+and install the git-flow extension alongside the other Git subcommands. If git
+is not on the system's `PATH`, it tries `/usr/libexec/git-core`. To explicitly
+override this setting in case you have installed Git in another location, use:
 
-	$ sudo make GIT_EXEC_PATH=/your/git/exec/path install
+	$ sudo make GIT_EXEC_PATH=/your/custom/path install
 
-Or simply point your `PATH` environment variable to your git-flow checkout.
+You rarely need to override this manually, the default 'make install' should do
+fine.
+
+Or simply point your `PATH` environment variable to your git-flow checkout
+directory.
 
 
 Please help out