Improve multipart HTTP/MIME entity file analysis.

Singular CR or LF characters in multipart body content are no longer
converted to a full CRLF (thus corrupting the file) and it also no
longer considers the CRLF before the multipart boundary as part of the
content.

Addresses BIT-1235.
Merge branch 'master' into topic/jsiwek/bit-1235
Merge remote-tracking branch 'origin/topic/jsiwek/bit-1235'

* origin/topic/jsiwek/bit-1235:
  Improve multipart HTTP/MIME entity file analysis.

BIT-1235 #merged