pgsql-server: Added SET DESCRIPTOR command.

Log Message:
-----------
Added SET DESCRIPTOR command.
Note that this still has some bugs. The functionality is there though, it's just a matter of fixing the bugs now.
Cleaned up error handling in preprocessor.

Modified Files:
--------------
pgsql-server/src/interfaces/ecpg/ecpglib:
descriptor.c (r1.7 -> r1.8)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/interfaces/ecpg/ecpglib/descriptor.c.diff?r1=1.7&r2=1.8)
execute.c (r1.34 -> r1.35)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/interfaces/ecpg/ecpglib/execute.c.diff?r1=1.34&r2=1.35)
extern.h (r1.8 -> r1.9)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/interfaces/ecpg/ecpglib/extern.h.diff?r1=1.8&r2=1.9)
pgsql-server/src/interfaces/ecpg/include:
ecpglib.h (r1.60 -> r1.61)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/interfaces/ecpg/include/ecpglib.h.diff?r1=1.60&r2=1.61)
pgsql-server/src/interfaces/ecpg/preproc:
descriptor.c (r1.19 -> r1.20)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/interfaces/ecpg/preproc/descriptor.c.diff?r1=1.19&r2=1.20)
extern.h (r1.60 -> r1.61)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/interfaces/ecpg/preproc/extern.h.diff?r1=1.60&r2=1.61)
pgc.l (r1.128 -> r1.129)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/interfaces/ecpg/preproc/pgc.l.diff?r1=1.128&r2=1.129)
preproc.y (r1.289 -> r1.290)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/interfaces/ecpg/preproc/preproc.y.diff?r1=1.289&r2=1.290)
type.c (r1.62 -> r1.63)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/interfaces/ecpg/preproc/type.c.diff?r1=1.62&r2=1.63)
variable.c (r1.34 -> r1.35)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/interfaces/ecpg/preproc/variable.c.diff?r1=1.34&r2=1.35)

Added Files:
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pgsql-server/src/interfaces/ecpg/test:
test_desc.pgc (r1.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/interfaces/ecpg/test/test_desc.pgc?rev=1.1&content-type=text/x-cvsweb-markup)