Add missing file to GETTEXT_FILES

This doesn't actually change the resulting set of strings, but better
be correct.

src/interfaces/ecpg/ecpglib/nls.mk

 # src/interfaces/ecpg/ecpglib/nls.mk
 CATALOG_NAME     = ecpglib
 AVAIL_LANGUAGES  = de es fr it ja pt_BR tr zh_CN
-GETTEXT_FILES    = connect.c error.c execute.c misc.c
+GETTEXT_FILES    = connect.c descriptor.c error.c execute.c misc.c
 GETTEXT_TRIGGERS = ecpg_gettext
 GETTEXT_FLAGS    = ecpg_gettext:1:pass-c-format