[libredwg] pslib no longer "required to build LibreDWG"

[Thien-Thi Nguyen]

Working on "make check" support, i just pushed this change:

    [test build] Check for pslib; build examples/dwg_ps only if present.
    
    * configure.in: Add checks for function `PS_open_file'
    in libps, and header file "libps/pslib.h".
    (HAVE_LIBPS): New AM_CONDITIONAL.
    * examples/Makefile.am (check_PROGRAMS): Remove `dwg_ps'.
    [HAVE_LIBPS] Add `dwg_ps' to `check_PROGRAMS'.
    [HAVE_LIBPS] (dwg_ps_SOURCES, dwg_ps_LDADD):
    Move these variables inside this conditional block.
    * README: Mention pslib non-critical requirement.

    (commit d36f1024d2001ece55558092ca8f3c8c4cd12dc)

Included is an update to the README that states more precisely the role
of pslib (it is needed only by examples/dwg_ps).  Could someone please
update the wiki accordingly?

thi