Bug 412345 - It's not possible to disable project-specific formatter
preferences

This patch improves the previous fix for the bug. The Code Formatter
preference page now uses correctly a working copy for the changed
settings and avoids additional flushes of the preferences on selection
change, which caused a number of problem in other preference types.

Bug: 412345
Change-Id: Ic0aacd7ff7f5bd87a774a9d5ba614df80ef1c6ba
Signed-off-by: Kaloyan Raev <kaloyan.r@zend.com>