Libecpg is used by programs built with ecpg (Embedded PostgreSQL for C) Use postgresql-dev to develop such programs.
lrwxrwxrwx 1 root root 14 oct 6 09:49 /usr/lib/libecpg.so.4 -> libecpg.so.4.1 -rwxr-xr-x 1 root root 41644 oct 6 09:50 /usr/lib/libecpg.so.4.1 lrwxrwxrwx 1 root root 21 oct 6 09:49 /usr/lib/libecpg_compat.so.1 -> libecpg_compat.so.1.2 -rwxr-xr-x 1 root root 13844 oct 6 09:50 /usr/lib/libecpg_compat.so.1.2 lrwxrwxrwx 1 root root 17 oct 6 09:49 /usr/lib/libpgtypes.so.1 -> libpgtypes.so.1.2 -rwxr-xr-x 1 root root 55792 oct 6 09:50 /usr/lib/libpgtypes.so.1.2