Fix Savannah bug #38235.

Work around a bug in pkg-config version 0.28 and earlier: If a
variable value gets surrounded by doublequotes (in particular values
for the `prefix' variable), the prefix override mechanism fails.

* builds/unix/freetype2.in: Don't use doublequotes.
* builds/unix/unix-def.in (freetype.pc): Escape spaces in directory
names with backslashes.
Don't require `gzip' module for `sfnt'.

Reported by Preet <prismatic.project@gmail.com>.

* src/sfnt/sfobjs.c (woff_open_font): Guard use of
FT_Gzip_Uncompress with FT_CONFIG_OPTION_USE_ZLIB.
[aflatin] Improve comment.
[autofit] Improve scoring algorithm for identifying stems.

Problem reported by Karsten Lücke <karsten.luecke@kltf.de>.

The new algorithm takes care of the width of stems: If the distance
between two segments is larger than the largest stem width, the
demerits quickly increase for larger distances.  This improves
hinting of slanted fonts (especially if the inner parts of serifs
have non-horizontal `shoulders'), avoiding false stem links.

* src/autofit/aflatin.c (af_latin_hints_link_segments): Use largest
stem width (if available) to compute better demerits for distances
between stems.
(af_latin_hints_detect_features): Pass stem width array and array
size.
(af_latin_metrics_init_widths): Updated to use original algorithm.
(af_latin_hints_apply): Updated to use new algorithm.

* src/autofit/aflatin.h: Updated.
* src/autofit/afcjk.c: Updated.