[bug fix] ECPG: freeing memory for pgtypes crashes on Windows

Hello,

Some user hit a problem with ECPG on Windows. The attached patch is a fix for it. I'd appreciate it if you could backport this in all supported versions.

The problem is simple. free() in the following example crashes:

char *out;

out = PGTYPESnumeric_to_asc(...);
free(out);

The cause is the mismatch of the version of C runtime library. The version of Visual Studio used to build the application was different from that for building PostgreSQL (libpgtypes.dll).

The fix is to add PGTYPES_free() in libpgtypes.dll, just like libpq has PQfreemem() described here:

https://www.postgresql.org/docs/devel/static/libpq-misc.html

Regards
Takayuki Tsunakawa