[base] Remove truncation in `FT_DivFix'.

* src/base/ftcalc.c (FT_DivFix): Updated.
[base] Use unsigned calculation in `FT_MulDiv'.

* src/base/ftcalc.c (FT_MulDiv): Updated to expand 32-bit range.
[base] Small optimization of `FT_MulFix'.

* src/base/ftcalc.c (FT_MulFix): Loosen up the condition for direct
32-bit calculations.
Minor.
Fix Savannah bug #43033.

* include/config/ftconfig.h, builds/unix/ftconfig.in,
builds/vms/ftconfig.h [FT_LONG64]: Do not disable the macro when
64-bit type is `long'.
Minor.
[truetype] Optimize DELTAP and DELTAC.

* src/truetype/ttinterp.c (Ins_DELTAP, Ins_DELTAC): Move ppem
calculations outside of the loop.
Don't use `register' keyword.  Fixes compiler warnings.

* src/base/ftcalc.c (FT_Add64) [!FT_LONG64]: Do it.
* src/gzip/inftrees.c (huft_build): Ditto.
* src/truetype/ttinterp.c (TT_MulFix14_arm): Ditto.
[truetype] Shortcut ppem calculations for square pixels.

* src/truetype/ttinterp.h (TT_ExecContextRec): New field
`cur_ppem_func' with a function pointer.
* src/truetype/ttinterp.c (TT_RunIns): Initialize `cur_ppem_func'
depending on the pixel geometry to either...
(Current_Ppem_Stretched): ... this for stretched pixels.
(Current_Ppem): ... or this for square pixels.
(DO_MPPEM, DO_MPS, Ins_DELTAP, Ins_DELTAC): Use `cur_ppem_func'.
Merge branch 'master' of git://git.sv.nongnu.org/freetype/freetype2