checksums: read sha1 and md5 into blocks

When calculating the checksums of a large file, we need to read it into
blocks (currently 16MB) to keep memory usage acceptable.
filetools.py: fix indenting
filetools.py: fix typo
filetools.py: use python 2.x stuff
filetools.py: python 2.4 comp. => don't use blocksize
address most remarks.
fix py24 issue with regtests
address a few more remarks
cleanup keyless entries code
introduce future and depracted options, and log.future
add misisng license header
fix remarks, using experimental rather then future.
pass experimental as build_option
moved options to the force section, added oldconfigstyle option
add unit tests for experimental and deprecated
filetools.py: nicier imports of checksums and explain magic number
filetools.py: use hashlib like wrapper for addler32 and crc32
default config location is decided in get_user_easybuild_dir()
repository.py: cleaner workflow in init_repository()
filetools.py: small changes after remarks