Fix portability issues in 86c43f4e.

INT64_MIN/MAX should be spelled PG_INT64_MIN/MAX, per well established
convention in our sources.  Less obviously, a symbol named DOUBLE causes
problems on Windows builds, so rename that to DOUBLE_CONST; and rename
INTEGER to INTEGER_CONST for consistency.

Also, get rid of incorrect/obsolete hand-munging of yycolumn, and fix
the grammar for float constants to handle expected cases such as ".1".

First two items by Michael Paquier, second two by me.