[ftvalid] Introduce FT_THROW() in FT_INVALID_XXX macros.

Original patch is designed by Werner Lemberg.  Extra part
for otvalid and gxvalid are added by suzuki toshiya, see
discussion:
http://lists.nongnu.org/archive/html/freetype-devel/2014-12/msg00002.html
http://lists.nongnu.org/archive/html/freetype-devel/2014-12/msg00007.html

* include/internal/ftvalid.h: Introduce FT_THROW() in FT_INVALID_().
* src/gxvalid/gxvcommn.h: Ditto.
* src/otvalid/otvcommn.h: Ditto.
[otvalid] Fix a naming convention conflicting with ftvalid.

Some prototypes in ftvalid.h use `valid' for the variables
typed as FT_Validator.  Their implementations in src/base/
ftobjs.c and utilizations in src/sfnt/ttcmap.c do similar.

Some macros in otvcommn.h assume the exist of the variable
`valid' typed as OTV_Validator in the caller.

Mixing these two conventions cause invalid pointer conversion
and unexpected SEGV in longjmp.  To prevent it, all variables
typed as OTV_Validator are renamed to `otvalid'.

* src/otvalid/otvcommn.h: Replace `valid' by `otvalid'.
* src/otvalid/{otvcommn.c, otvbase.c, otvgdef.c, otvgpos.c,
otvgsub.c, otvjstf.c, otvmath.c}: Replace `valid' by `otvalid'
if it is typed as OTV_Validator.
[gxvalid] Fix a naming convention conflicting with ftvalid.

See previous changeset for otvalid.

* src/gxvalid/{gxvcommn.h, gxvmort.h, gxvmorx.h}: Replace
`valid' by `gxvalid'.
* src/gxvalid/{gxvbsln.c, gxvcommn.c, gxvfeat.c, gxvjust.c,
gxvkern.c, gxvlcar.c, gxvmort.c, gxvmort0.c, gxvmort1.c,
gxvmort2.c, gxvmort4.c, gxvmort5.c, gxvmorx.c, gxvmorx0.c,
gxvmorx1.c, gxvmorx2.c, gxvmorx4.c, gxvmorx5.c, gxvopbd.c,
gxvprop.c, gxvtrak.c}: Replace `valid' by `gxvalid' if
it is typed as GXV_Validator.