skype: mention --plugindir quirk in HACKING

As skype support always gets built as plugin, option is required
for running tests without installing plugin to the system.
skype.test: do proper cleanup of skyped process despite possible exceptions, keep pexpect.log
skype: make chdirs work more reliably between tests
skype: use argparse instead of getopt for CLI in skyped
skype: add --dont-start-skype option

For cases when case skype start/stop/restart is being handled externally.
Skype4Py seem to be able to handle client going on/off.
skype: add ATTACH_GDB env flag, extend hacking instructions with info on pexpect/gdb
skype: add newline to all the lines emitted
skype: cleanup of the send() code

Use socket.sendall(), as send() is not guaranteed to send all
the data passed (though it should generally work that way with
blocking sockets).
Use more robust, obvious and idiomatic loop conditions.
Cleanup redundant imports and variables.
skype: don't do retries on send() on socket errors with gobject

As it's a blocking socket, I imagine there might be only EINTR
errors from signals, which don't seem to be used here.
I think the same tweak can be applied to select() code, but
I don't run it, so no idea if Skype4Py threads might make such loop
necessary there.
skype: handle socket errors during tls session negotiation in a graceful way

Before this patch, such errors (which happen 1/4 times here) lock
skyped forever, producing traceback (and hanging because threads
in python).
Proper fix would be to see why these happen (might be ssl handling
in the plugin), but that's no excuse not to handle socket errors
without crashing the daemon.
skype: handle only socket errors in send()
skype: check for truncated commands on receiving
skype: rename these tests, these are about we are added, not about we add
skyped: print again the config file path
test skype_add_buddy()
skype_buddy_action_list: fix missing hangup in help output
test skype_buddy_action_list()
test skype_set_mood_text()
skype tests: run all tests with a single skyped config

This makes them a bit faster, and there is no need to have separate
skyped configs for each test ATM.
Clean up set_my_name API implementations