Fix failure to compile on Windows due to 2012-07-27T06:04:35Z!dmantipov@yandex.ru.

Fix failure to compile on Windows due to 2012-07-27T06:04:35Z!dmantipov@yandex.ru.

 src/lisp.h (enum constype): Use CONSTYPE_HEAP and CONSTYPE_PURE for
 enumeration constants, as PURE and HEAP are too general, and clash
 with other headers and sources, such as gmalloc.c and the
 MS-Windows system headers.  All users changed.