mediafire (download): fix anonymous download
letitbit: add probe support
hotfile: add probe support

Initial patch: Stefan Meier
rapidshare (probe): enhance by using API
ryushare: add probe support
netload_in: add probe support

This uses the official API which requires an key. For now, a
fixed key is used although I'm not sure whether this is intended.

If problems arise we'll have to add an account requirement, so
each account's own API key can be retrived and used.
depositfiles (upload): change default upload url (depositfiles.com => dfiles.eu)
megashares: add probe support
netload_in (probe): fix alternate link format
download.sh: accept file:// protocol as valid URL from xxx_download() module function

This trick is actually used by mega.
putlocker (download): it seems that video streaming content has always the "Download File" button

Original file can be downloaded, don't need to distinguish "online streaming" and "direct download" anymore.
core.sh (grep_block_by_order): use "grep -c" instead of "sed + tr"

This is faster!
plowup: add sanity check, check if returned URL contains \r
docs (plowdown.1): enhance documentation for --captchaprogram
4shared (upload): quick upload fix
4shared (upload): fix, forget to drop temp debug
download.sh (mark_queue): fix unmarked url (if it contains backslash characters)
mediafire (login): send referrer so website does not refuse login
mediafire (download, probe): small rewrite to enhance features

- new functions "mediafire_extract_id" and "mediafire_is_file_id"
- fix detection of direct download links
- add error message when file links are given to plowlist or
folder links are given to plowdown

Note: Detection of folder vs. file links is quite fragile. It relies
on folder IDs to consist of exactly 13 digit/letters. This is true
for all links I found but need not be a general fact.
mediafire: add probe support