Improvements in rtags-show-target-in-other-window (rtags.el).

Add optional parameter to use an existing window and not split a new one.
Add optional parameter to center the text in the window displaying the target.
rtags.el : improvements in taglist.

Add option to open the taglist in the current window (to avoid deleting other windows).
Change appearance of categories.
Fix processing unsaved files. Support for searching for declaration first.
rtags.el - implement reparsing of unsaved files.
rtags.el : implement rtags-display-summary, rtags-get-summary-text.
rtags.el : style issues; remove some unnecessary '(interactive)'.
rtags.el : revert some changes.
rtags.el : fix infinite loop when a file is not indexed.
rtags.el : avoid reparsing unsaved files if there were no changes since last parsing.

Also make some 'rc' calls silent.
Remove unused function.