To support OTP release upgrades I have added support for building
upgrade packages. Support for this is included in the
rebar_upgrade module, specifically generate_upgrade/2. It requires
one variable to be set on the command line 'previous_release' which
is the absolute path or relative path from 'rel/' to the previous
release one is upgrading from. Running an upgrade will create the
needed files, including a relup and result in a tarball containing
the upgrade being written to 'rel/'. When done it cleans up the
temporary files systools created.

Usage:
$ rebar generate-upgrade previous_release=/path/to/old/version

This also includes a dummy application that can be used to test
upgrades as well as an example.

Special thanks to Daniel Reverri, Jesper Louis Andersen and
Richard Jones for comments and patches.

abnfc is an ABNF parser generator.
Options are:
	- doc_root (defaults to "src")
	- out_dir (defaults to "src")
	- source_ext (defaults to ".abnf")
	- module_ext (defaults to "")

Erroneously put rebar_pre_script at the end of the app_dir modules
list in the previous commit.

Add support for compiling ASN.1 files with asn1ct.
Patch from Ruslan Babayev.

defaults to compiling from templates/*.dtl to ebin/*_dtl.beam
see top of rebar_erlydtl_compiler for configuration options

Added compile check for app name.
Added compile check for app modules

--HG--
rename : src/rebar_app_installer.erl => src/rebar_otp_app.erl

--HG--
rename : src/rebar_doterl_compiler.erl => src/rebar_erlc_compiler.erl