Backporting various fixes in Advanced Find and Replace:

Backporting various fixes in Advanced Find and Replace:
- Now the cursor is visible while at the rightmost part of a regexp inset.
- Now a regexp inset with a \backslash or braces is previewed correctly.
- Disabled possibility to type macros in regexp-mode.
- Now backslash-prefixed regexps like "\s", "\d", etc., are all understood by Advanced F&R.
- Now Adv. F&R correctly interprets escape sequences within regexp insets, e.g., \\ or \(,
  for finding characters with a special meaning in regular expression context (\^()[]).

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/branches/BRANCH_2_0_X@39136 a592a061-630c-0410-9148-cb99ea01b6c8