Readline linking update

Readline linking update

Modify linking of readline library. Create new  substituted varible
READLINE_LIBS - readline library is linked ONLY with tools that really use
it - i.e. lvm. (Static lvm does not use readlin).
Previous behaviour put this library into the variable LIBS and thus
linked it with all created object files of lvm project (i.e. plugins...).

READLINE detection is simplified.

Termcap library is linked in only if readline library doesn't have its own
dependency (i.e. old distributions).