Add test for checking generated .tac file

It checks that .tac file is valid Python script by exec()-uting it with
mocked globals imports, such as twisted.application.service.Application
and buildslave.bot.BuildSlave.
Then it checks, that Application was created and stored in global
variable "application" (as .tac specification requires); checks that
BuildSlave created with passed arguments and attached to application.
Add tests for basedir containing quotes, spaces and backslashes

Quotes test failing with master Buildbot.

In one of the older Buildbot releases I tried to create slave on Windows
end ended with invalid .tac file due to something like this:

  basedir = 'C:\basedir\'

Looks like this is fixed in master, but adding test won't hurt.
Fix handling basedir with quotes
Add tests for invalid --umask and --allow-shutdown options

Currently fails.
Handle invalid --umask and --allow-shutdown options
Add test for handling special characters in all options fields

Currently fails.
Fix options fields writing in .tac file
Write "log-size" as numeric, since it's always integer
Merge branch 'slave_tac_check_and_fix' of git://github.com/vrutsky/buildbot