popen and pclose redefinitions causing many warning in Windows build

Hi all,

Since commit a692ee5, code compilation on windows is full of warnings
caused by the re-definitions of popen and pclose:
In file included from ../../../src/include/c.h:1028:0,
                 from ../../../src/include/postgres.h:47,
                 from analyze.c:25:
../../../src/include/port.h:312:0: warning: "popen" redefined [enabled
by default]
In file included from ../../../src/include/c.h:81:0,
                 from ../../../src/include/postgres.h:47,
                 from analyze.c:25:
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/4.7.0/../../../../x86_64-w64-mingw32/include/stdio.h:48
9:0: note: this is the location of the previous definition
In file included from ../../../src/include/c.h:1028:0,
                 from ../../../src/include/postgres.h:47,
                 from analyze.c:25:
../../../src/include/port.h:313:0: warning: "pclose" redefined
[enabled by default]
In file included from ../../../src/include/c.h:81:0,
                 from ../../../src/include/postgres.h:47,
                 from analyze.c:25
The patch attached fixes that.
Regards,
--
Michael