These functions will be necessary in rebar_eunit.erl, too.

Automatically include modules with callback attributes in
erl_first_files.

Generate .hrl files into include from SNMP MIB files.
Change the order of so .mib files are built before .erl
This is necessary since .hrl files are generated from
the .mib files.
The generated .bin and .hrl files are deleted by clean.

This is a cleaned up version of a patch originally
sent to the rebar mailing list by David Nonnenmacher.

Calling erlang:system_info(wordsize) yields the internal word size of
the Erlang emulator. But due to the halfword emulator, need to pass
{wordsize, external} instead to get the word size, or pointer size, as
seen by external code such as NIFs. The halfword emulator has 4 byte
internal words but 8 byte external words due to 64-bit compilation,
which means NIFs for the halfword emulator also have to be compiled
64-bit. But just passing wordsize is equivalent to passing {wordsize,
internal}, which does not indicate the pointer size for the halfword
emulator.

Older versions of Erlang do not support {wordsize, external}, though,
so continue to pass just wordsize for those versions.

Add no_debug_info option.
Remove debug_info=1 option.

If an app uses -include_lib for its own included files, compilation
fails if the app directory isn't in $ERL_LIBS because code:lib_dir/1
will return an error. An absolute path needs to be added to code path
instead of just "ebin".

Prevent overlooking a compilation warning by removing the target beam
file after fail_on_warning failure.

- Check the existence of first_files and fail if they are not present
 - Get first_files lists from local instead of inherited config
   definitions, since they only make sense in the local context

Using rebar's commandline, enable/disable 'debug_info' for
compilation. This feature if added to all rebar compilers could help
simplify and standardize this common use case for all rebar build
targets.

Modify rm_rf and cp_r to work when {win32,_} = os:type().
Simplify rm_rf to only accept one filename, directoryname or wildcard.
Add unit tests to ensure a similar behaviour on windows and unix.

Thanks to tuncer for guidance and feedback.

The previous code in rebar that was trying to ensure that parse
transforms and behaviours were compiled first doesn't work with multiple
compiler workers because of the possiblity of one of the workers
compiling a file that needs a parse transform or a behaviour at the same
time another worker is compiling that same parse transform or behaviour.

The solution this patch implements is to append any parse transforms and
any behaviours (in that order) to erl_first_files to ensure that they
are compiled before any regular files. This patch won't break any
currently working uses of erl_first files because we only append to the
list, so anything in erl_first_files is still compiled before anything
else.