fix evas image loading error reporting.

fix evas image loading error reporting.

Evas image load was always reporint "generic" error, since it was
disconnected from actual loader modules.

This commit will break the module loader API (as it's restricted to
inside Evas, this should be no problem). The return was turned into
"Eina_Bool" for clarity, while an extra "int *error" is responsible to
report errors. This approach was choosen to force compiler warnings
and to try avoid mistakes as EINA_FALSE == EVAS_LOAD_ERROR_NONE and
thus we'd get opposite behavior if something slips.

Most loaders play well, except by eet that does not provide means to
know if the file open failed due missing file, incorrect format or
corrupted file :-(

Please report any issues. I added eina_log debugging to loader
functions, just run your Evas application as:

     EINA_LOG_LEVELS=evas_main:4 your_app

SVN revision: 44666