Add support for minimum OTP versions.

Since you can't really do math with regexps and it's a pain to
repeatedly update the config for each new version or erlang, I wanted
to add support for minium OTP versions.  This is a fix for
https://github.com/basho/riaknostic/issues/38
Merge branch 'master' of github.com:hyperthunk/rebar
Finalize port_compiler deprecations
Fix indenting
rebar_deps: use xconf for deps_dir
rebar_rel_utils: remove two lines of noop
Add Community section to README

Links to the mailing list, issues page, and wiki are included,
plus information relative to the IRC channel.
Re-format README changes
relative libs in RELEASES file
Rename old eunit compile options for consistency with test-compile
Fix trivial comment typo
Fix -c typo (Noticed-by: Joe Norton)
Fix -D handling
Fix R13B03 build (Reported-by: Sergey Nartimov)
Add rebar.hrl R13B04 TODO

We have to rename ?FAIL to ?ABORT once we require at least R13B04 for
building rebar. Macros with different arity were not supported by the
compiler before 13B04.
No need to re-specify default escript_shebang in rebar.config
Quote paths in Windows runner script

This allows the node to run in paths which include special characters,
for example 'C:\Program Files (x86)\Product Name'
Add experimental notice to test-compile and shell
Quote EUnit User's guide about _tests.beam handling
Refactor setup_env rebar_config funs