pgsql: - Made several variables "const char *" instead of "char *" as

Log Message:
-----------
- Made several variables "const char *" instead of "char *" as proposed by Qingqing Zhou <zhouqq(at)cs(dot)toronto(dot)edu>.
- Replaced all strdup() calls by ECPGstrdup().
- Set ecpg library version to 5.2.
- Set ecpg version to 4.2.1.

Modified Files:
--------------
pgsql/src/interfaces/ecpg:
ChangeLog (r1.294 -> r1.295)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/ChangeLog.diff?r1=1.294&r2=1.295)
pgsql/src/interfaces/ecpg/ecpglib:
Makefile (r1.33 -> r1.34)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/ecpglib/Makefile.diff?r1=1.33&r2=1.34)
connect.c (r1.26 -> r1.27)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/ecpglib/connect.c.diff?r1=1.26&r2=1.27)
descriptor.c (r1.12 -> r1.13)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/ecpglib/descriptor.c.diff?r1=1.12&r2=1.13)
execute.c (r1.43 -> r1.44)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/ecpglib/execute.c.diff?r1=1.43&r2=1.44)
prepare.c (r1.14 -> r1.15)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/ecpglib/prepare.c.diff?r1=1.14&r2=1.15)
pgsql/src/interfaces/ecpg/include:
ecpglib.h (r1.63 -> r1.64)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/include/ecpglib.h.diff?r1=1.63&r2=1.64)
pgsql/src/interfaces/ecpg/preproc:
Makefile (r1.114 -> r1.115)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/preproc/Makefile.diff?r1=1.114&r2=1.115)