cscope: 15..7 bugfix release

Cscope is a text screen based source browser

cscope 15.7 is tagged and released

Minor bugfix release including various fixes:
*Some build file updates for newest autotools
*Fixes for some screen redraw corner cases
*Fixes for newline handling in dir names
*Fixes for non-readable files
*A few crash fixes
*Fixes to handle hpp/hxx files
*Fixes to clean tmp files on exit
*Minor lexer fixes
*Documentation enhancement

As always, check the ChangeLog for details.

Thanks all!