crc32sum: use getpagesize()

Call to getpagesize() to get the system page size instead of
defaulting to a hardcoded value of 4KB.
crc32sum: substitute printf() with fprintf()
crc32sum: fix digest_*() return type and error path

In digest_*() change return type to match that of crc32().
Also, fix the error path in digest_file() to release resources.
Initial commit
ccr32sum: read CRC32 sums from FILE and check them

The function digest_check() reads a file containing tuples of
<hash, filename>, one each line, and computes the hash value of
the file to check its integrity.