Clean up some includes

Clean up some includes

We no longer include Csocket.h in main.h because only few files actually need
it. (Only HTTPSock.h and Timers.h)

We also clean up some includes in Timers.h. It didn't actually include
the file it needed.

Oh and this also adds a warning to main.h if PATH_MAX is undefined. If this
happens, it is most likely a bug that needs to be addressed. (some missing
includes, I'd guess)

git-svn-id: https://znc.svn.sourceforge.net/svnroot/znc/trunk@1099 726aef4b-f618-498e-8847-2d620e286838