Some bugfixes for numerical library.

src/interfaces/ecpg/ecpglib/execute.c

src/interfaces/ecpg/include/decimal.h

src/interfaces/ecpg/include/pgtypes_error.h

src/interfaces/ecpg/pgtypeslib/numeric.c

src/interfaces/ecpg/preproc/Makefile

src/interfaces/ecpg/preproc/ecpg.c

src/interfaces/ecpg/test/num_test.pgc

src/interfaces/ecpg/test/test1.pgc