Allow a U. F. O. to omit fontinfo.plist.
View/Combinations/KernPairs mistakenly right-to-left

Issue #1811 mentioned trying to understand kern pairs by consulting the
View / Combinations / Kern Pairs UI dialog, in addition to the other
dialogs that can display kern pairs.  While tracing reporters steps with
their cited TTF I noticed something odd.  For just 'some' kern pairs,
the character pair would be displayed in reversed order and
right-justified.  Very much as though FF thought right-to-left display
was required.

I verified this behavior with the ./tests/fonts/Caliban.sfd file, where
for example 'sometimes' "Lv" would be displayed right-justified as "vL",
"Fo" would be "oF", etc.  This would happen for a small random assortment
of character pairs.

Disabling setting of the `r2l` flag within `fontforgeexe/combinations.c`
routine `CheckLeftRight()` did not stop the problem, as breakpoints on
the right-to-left display code in `KP_ExposeKerns()` found some pairs
had the flag set anyway.

Checking further found that when the `r2l` flag was added in 2002, no
additional initialization code was put into `KPBuildKernList()` or
`void KPBuildAnchorList()`.  Uninitialized allocated memory would
occasionally 'set' the flag `r2l`.

This change uses `calloc()` vs. `malloc()`, and has `CheckLeftRight()`
always set the flag to either true or false.  This guarantees flag is
defaulted to false, and is left set correctly on each call.

Tested before and after against the Caliban.sfd file.  All pairs now
consistently displayed correctly.
Pretty message on TTC open with missing/bad font names

Very minor change to make font selection a bit more understandable,
when opening a TTC file where some/all font names in the TTC are
missing or bad.  User is slightly reassured to see there are multiple
separate fonts within the TTC.

For each missing font name, a line of "Unknown font name NN" is
substituted in the list presented by the dialog "There are multiple
fonts in this file, pick one".  If user want to examine them one by
one they are at least assured they are picking different fonts.

Tested against broken downloaded font /tests/fonts/mingliu.ttc and
against the correct mingliy.ttc file from Windows.
Allocate user_data for the point information window for Spiro since the window destructor likes to free it. Also eliminate the duplicate call to the window destructor at the end of SpiroPointGetInfo since the event loop handles that.
Merge pull request #1842 from fontforge/spiro_point_info_crash_1

Avoid crashes when closing the point info window in Spiro mode.
Merge pull request #1841 from tshinnic/1820_ttf_short_crash_2

Pretty message on TTC open with missing/bad font names
Merge pull request #1840 from tshinnic/view_combin_kern_pair_1

View/Combinations/KernPairs mistakenly right-to-left
Merge pull request #1833 from fontforge/ufo_optional_fontinfo_1

Allow a U. F. O. to omit fontinfo.plist.
Merge pull request #1834 from rrthomas/master

Allow native test scripts to return status, and fix so they work (redo PR #1780 to fix issue #1779)
Remove WINDOWS_CROSS_COMPILE

This was only used to avoid a necessary check in collab builds on
Windows. @jtanx, who does the Windows binaries, says collab currently
isn’t building on Windows anyway.