missing time.h include in psql/command.c since the addition of \watch

Hi,

our internal testbuilds show a new warning on windows:
src\bin\psql\command.c(2617): warning C4013: 'time' undefined; assuming extern returning int
[C:\jenkins\workspace\andres_git.postgresql.org_windows\BT\release\SL_OS\windows\TA\x86\TO\xp\psql.vcxproj]
src\bin\psql\command.c(2619): warning C4013: 'asctime' undefined; assuming extern returning int
[C:\jenkins\workspace\andres_git.postgresql.org_windows\BT\release\SL_OS\windows\TA\x86\TO\xp\psql.vcxproj]
src\bin\psql\command.c(2619): warning C4013: 'localtime' undefined; assuming extern returning int
[C:\jenkins\workspace\andres_git.postgresql.org_windows\BT\release\SL_OS\windows\TA\x86\TO\xp\psql.vcxproj]

Looking at command.c its neither surprising that we get that warning,
nor that we don't get it on non-windows builds. Those get time.h via
portability/instr_time.h.

So it seems we should add a time.h include to command.c. Trivial patch
for that attached.

Not sure why that warning isn't visible on the buildfarm though...

Greetings,

Andres Freund

--
 Andres Freund                       http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services