Address issue #1427 by removing PListCreate in ufo.c.
Merge pull request #1428 from fontforge/ufo_libxml2_1

Remove PListCreate in ufo.c.
Work through the compiler warnings and take action as necessary.

This fixes most of the warnings, except for:
* Any collab code
* fontforge/ufo.c (skipped)
* encoding.c: Assigning const parameter AdobeStdEncoding to what may be free'd
  - No easy way to resolve this
* charview.c: 12910 - Should this be cast or converted?
  > mblist_nomm[i].ti.text_untranslated = mblist_nomm[i].ti.text;
* cvpalettes.c: Redefinitions of MID_*
* metricsview.c: selectUserChosenWordListGlyphs - Comparing GArray pointer against 0 / -1 / -2 ?
* windowmenu.c: Same question as for charview.c
  > e.g:
  > windowmenu.c:270:33: warning: assignment makes pointer from integer without a cast
      mb[i].ti.text_untranslated = mb[i].shortcut;
Work through the compiler warnings in ufo.c

These functions could not be declared with const SplineChar* because one
or more functions that they subsequently call modify that parameter:
* UFOOutputFontInfo
* UFOOutputFeatures
* WriteUFOFont

The most notable example is a call which leads to SFReadChar being called.
There may be other functions which also modify the parameter, but tracing
the calls is tedious.