core.sh (create_tempfile): consider --temp-directory if specified

Changes:
- plowup: add --temp-directory command-line option
- core.sh: add 'D' type for argument parsing (check for directory with write access)
- man pages updated

Fixes issue 959.
turbobit (login, download): fix, upstream modified

Also changes the input style of 'parse' commands from 'echo'
piping to here strings to prevent SIGPIPE problems in the
future.

see issue 964
core.sh (parse_form_input_by_*): accepts spaces around '=' in HTML attributes

For example:
<input name= "yes"  ...>
<input name = "yes" ...>
<input name ='y s'  ...>
<input name = y     ...>

are valid.

Thanks to Jan for this.
ryushare (download): fix, upstream modified

Ryushare uses Solvemedia captchas now.

see issue 965
letitbit (download): fix SIGPIPE bug