i18n Makefile for 1.3.0 does not handle DESTDIR correctly

Hi Dave,

the Makefile in i18n pgadmin3 directory does not handle properly DESTDIR
and tries to install files directly in the prefix.

Example of failed session:
...
/usr/bin/make install DESTDIR=/home/pga3/1.3.0/pgadmin3-1.3.0/debian/tmp
make[1]: Entering directory `/home/pga3/1.3.0/pgadmin3-1.3.0'
Making install in i18n
make[2]: Entering directory `/home/pga3/1.3.0/pgadmin3-1.3.0/i18n'
make[3]: Entering directory `/home/pga3/1.3.0/pgadmin3-1.3.0/i18n'
make[3]: Nothing to be done for `install-exec-am'.
/home/pga3/1.3.0/pgadmin3-1.3.0/config/install-sh -d
/usr/share/pgadmin3/i18n
mkdir: cannot create directory `/usr/share/pgadmin3': Permission denied
make[3]: *** [install-data-local] Error 1
make[3]: Leaving directory `/home/pga3/1.3.0/pgadmin3-1.3.0/i18n'
make[2]: *** [install-am] Error 2
make[2]: Leaving directory `/home/pga3/1.3.0/pgadmin3-1.3.0/i18n'
make[1]: *** [install-recursive] Error 1
make[1]: Leaving directory `/home/pga3/1.3.0/pgadmin3-1.3.0'
make: *** [install] Error 2

Would this be possible to correct this please ? The patch attached
should do the trick although not well tested.

Regards,
Raphaël