Make ecpg thread safe.

configure.in

doc/src/sgml/ecpg.sgml

doc/src/sgml/installation.sgml

src/interfaces/ecpg/ecpglib/Makefile

src/interfaces/ecpg/ecpglib/connect.c

src/interfaces/ecpg/ecpglib/data.c

src/interfaces/ecpg/ecpglib/descriptor.c

src/interfaces/ecpg/ecpglib/error.c

src/interfaces/ecpg/ecpglib/execute.c

src/interfaces/ecpg/ecpglib/extern.h

src/interfaces/ecpg/ecpglib/memory.c

src/interfaces/ecpg/ecpglib/misc.c

src/interfaces/ecpg/ecpglib/prepare.c

src/interfaces/ecpg/ecpglib/typename.c

src/interfaces/ecpg/include/sqlca.h

src/interfaces/ecpg/preproc/Makefile