add easyconfig for GCC (.eb spec files for GCC v4.5/4.6/4.7 with and without CLooG/PPL support + patch for mpfr 3.1.0)

tested with GCC v4.5/4.6/4.7 both with and without CLooG/PPL support;
various other improvements/bugfixes along the way

adjust setup scripts so it creates both the easyblocks and easyconfigs directories, squash the '_other_' and '0-9' easyblocks subdirs into '0' (refs #125)

adjust setup scripts so it creates both the easyblocks and easyconfigs directories, squash the '_other_' and '0-9' easyblocks subdirs into '0'

add strict version check for lower than v4.5 and option to skip with skipversioncheck, warn when building with 4.8 or higher

get rid of code that sets C_INCLUDE_PATH, LD_LIBRARY_PATH and LD_RUN_PATH for GMP, since it makes no difference w.r.t. the __gmp_get_memory_functions undefined references (real problem was that path of other libgmp.so was present in LD_LIBRARY_PATH)

add support to make LTO fully optional (required for GCC v4.5 build without libelf installed)

add support for setting maximum degree of parallelism (e.g. for CLooG build in GCC, that doesn't seem to handle parallelism of 7 well, but 3 seems fine)

get rid of getlogin == 'root' check, it's useless and creates problems when easybuild is used from within a job (see http://stackoverflow.com/questions/4399617/python-os-getlogin-problem)

make bootstrap build non-optional, since it's required for stand-alone build
add check for unrecognized configure options
add version checks for CLooG/PPL

 -Wl,--start-group lib, lib, lib, -Wl,--end-group gives problems with pkg-utils
 we can pack these into one argument like this:
 -Wl,--start-group,lib,lib,lib,--end-group

this can be enabled with toolkitopts{'pack-groups': True} in a .eb file

derive full easyblock path if it's only specified by name, fix bug and improve error handling (refs #214)

derive full easyblock module path when easyblock is only specified by name, return created instance, better error handling

replace 'mod' in .eb files with 'easyblock'
avoid use of exec in get_instance (see #214)