Clean up SOCI_POSTGRESQL_NOPARAMS name.

Clean up names and uses of SOCI_POSTGRESQL_NOPARAMS vs SOCI_PGSQL_NOPARAMS
Close #120
Fix prepared insert statement

This fix also allows to use data exchange with custom type.
Fixes #117

(Original commit message amended by Mateusz Loskot)
Add latest hotfixes to CHANGES
Report prepared insert test status after session is cleaned up
Do not deallocate non-existing prepared statement

This is refinement of fix submitted in #107 and fixes #116
Add latest hotfixes to CHANGES

Close #116
[ci skip]