Postscript characters overlapping

Hi all,

I've noticed that postscript export may produce documents with
overlapped chars, specially when using accented chars. I've been looking
into xap_unixPSGraphics.cpp file and have discovered that there's an cumulative
rounding error problem. I enclose the patched file for inclusion in
future releases.

Note: This is the first time i'm posting here. Please let me know if I'm
not doing things right!