Output maf version number with "--mafversion"

[hiroshinoji]

Incomplete implementation for #89.

Currently maf.py obtain the revision number of git, but now maflib cannot access to it.
We have to implement core.ExpOptionsContext.init. The version is now a constant of in maf.py, but we cannot access this number from maflib. Maybe we have to make an auto generated file in .waf-*/maflib directory to save some constants.

[hiroshinoji]

Currently it is partly working but not complete.

To check version numbers, core.py has constants MAFVERSION and MAFREVISION which are inserted by generate_maf.py. These versions are checked in maf.py when loading. generate_maf.py also assigns version numbers to maf.py so these should be consistent.

The current problem is, when using maf in the git repository (where maflib exist) core.py is loaded from not hidden directory (.waf-.../maflib) but the maflibdirectory. The original maflib/core.py doesn't have version numbers so it cannot load version numbers correctly.

[hiroshinoji]

The problem above is rather complicated. First, I found a snippet in waflib where sys.path is written temporarily during executing main waf logic:
http://docs.waf.googlecode.com/git/apidocs_17/_modules/waflib/Context.html#load_module

For this, when loading maf.py, maflib/core.py has a precedence over .waf-*/maflib/core.py.

We skip this problem by not checking version in maf.py if the user is probably developing maflib. If the loaded version is not filled, that means maflib is loaded from the current directory, in that case we assume the user is developing maflib.

[beam2d]

Thanks for supporting versioning. LGTM with one comment.

If one migrates from old version that does not define MAFVERSION to the new version with MAFVERSION, an exception AttributeError: 'module' object has no attribute 'MAFVERSION' occurs. It should be more verbose (e.g. catch it and print some verbose message).

[beam2d]

LGTM!