Fixed bug #621531 (const & volatile confusion in the type chain).

Fixed bug #621531 (const & volatile confusion in the type chain).
DCL_PTR_CONST, DCL_PTR_VOLATILE, & IS_PTR_CONST now exclusively
refer to the const or volatile state of the pointer itself.

* src/SDCCast.c
* src/SDCCglue.c
* src/SDCCicode.c
* src/SDCCsymt.c
* src/SDCCval.c
* src/SDCC.y
* src/SDCCsymt.h
* src/pic/gen.c
* src/pic/ralloc.c
* src/pic16/gen.c
* src/pic16/ralloc.c
* support/regression/tests/const.c

git-svn-id: https://sdcc.svn.sourceforge.net/svnroot/sdcc/trunk/sdcc@2885 4a8a32a2-be11-0410-ad9d-d568d2c75423