fixed possible corruption of first bytes in file.

the recv() command to fetch filename_size and filename may fetch file
data which is later ignored (not written to file).
also used uint32_t and ntohl/htonl to serialize filename_size.
Merge pull request #14 from bahaa-aidi/filename_fix

fixed possible corruption of first bytes in file.
changed BCP_CODE and port to use unit32_t and ntohl
added a few bash commands, thanks to André Gil