Remove eval-when-compile for loading cl.el

Because skype.el uses some cl function.
And add buffer local variable for it.
Use with-current-buffer instead of save-excursion + set-buffer
Add declarations of buffer local variable

Buffer local variables should be declared by defvar, defcustomize etc.
Fix order of variable, function declaration

'declaration' should precede 'use'.
Use declare-function for function defined at other file
Fix for calling skype--layout-chatmsg-function

We should use 'funcall', becaues it is variable, not function.
Merge pull request #4 from syohex/byte-compile-warnings

Byte compile warnings