- Changed find_colon() into check_for_hostspec(), extending it to

  understand the rsync:://HOST:PORT/PATH format, allowing all HOSTs
  to be IPv6 literal addresses enclosed in '[' and ']', and changing
  it to return the 3 parts of the spec separately (host, port, and
  path).
- Relocated the code that handles the sanitation and validation of
  the files_from arg in order to make its placement a little more
  logical.
- Replaced remote_filesfrom_file with filesfrom_host, which makes
  the value of the files_from variable more intuitive.