don't leave broken $(PKG_FILE) on a error

so that next time this tries to fetch it again.
Add release support to erlang.mk

No special configuration is needed, the release will be built
automatically if a relx.config file is found.
Merge branch 'wget-error' of git://github.com/yamt/erlang.mk
Don't leave broken $(RELX) on error either

This will do until we stop using wget.
Small verbosity tweaks
Tolerate spaces in .app.src {modules, []} tuple
Running 'make clean-all' has errors if a dep has no Makefile

Create a project with a dependency that has no Makefile such as wooga/eredis.
Do 'make all' then 'make clean-all' to get an error. This patch checks for the
presence of the Makefile before attempting to run 'make clean', however, it does
not attempt run 'rebar clean' or other commands instead.
Merge branch 'master' of git://github.com/jaynel/erlang.mk
Merge branch 'fix-modules-space' of git://github.com/RJ/erlang.mk