Issue 4902: Improve `-dgs-load-fonts` option for TTF that doesn't have glyph names

Issue 4902/2: Improve `-dgs-load-fonts` option for TTF

`-dgs-load-fonts` loads fonts via Ghostscript.
However, if a TrueType font (TTF)
that does not have glyph names is loaded via Ghostscript,
all characters are shown in TOFU.

This commit lets `-dgs-load-fonts` loads those fonts
in a way that is not via Ghostscript.

Issue 4902/1: Add procedure `ly:has-glyph-names?`

This commit adds procedure `ly:has-glyph-names?`
to check whether or not a font has glyph names.

*This patch requires Issue 4900 and Issue 4901.*
https://codereview.appspot.com/301990043
https://codereview.appspot.com/299360043

[lemzwerg, 2016-06-19 18:49:53]

LGTM.

https://codereview.appspot.com/302000043/diff/1/lily/open-type-font-scheme.cc
File lily/open-type-font-scheme.cc (right):

https://codereview.appspot.com/302000043/diff/1/lily/open-type-font-scheme.cc...
lily/open-type-font-scheme.cc:216: bool has_glyph_names = face->face_flags &
FT_FACE_FLAG_GLYPH_NAMES;
bool has_glyph_names = FT_HAS_GLYPH_NAMES(face);

[trueroad, 2016-06-19 22:02:48]

Use FT_HAS_GLYPH_NAMES

[trueroad, 2016-06-19 22:05:07]

Thank you for your reviewing.

https://codereview.appspot.com/302000043/diff/1/lily/open-type-font-scheme.cc
File lily/open-type-font-scheme.cc (right):

https://codereview.appspot.com/302000043/diff/1/lily/open-type-font-scheme.cc...
lily/open-type-font-scheme.cc:216: bool has_glyph_names = face->face_flags &
FT_FACE_FLAG_GLYPH_NAMES;
On 2016/06/19 18:49:53, lemzwerg wrote:
> bool has_glyph_names = FT_HAS_GLYPH_NAMES(face);

Done.

[trueroad, 2016-06-27 14:59:18]

I've pushed to staging.

Issue 4902/1: Add procedure `ly:has-glyph-names?`
commit 9437884ac32029c7166ab54cb4f727232b7cdc3c

Issue 4902/2: Improve `-dgs-load-fonts` option for TTF
commit b060b5bac8cb49ab80f6ea31410725340423e6f7