Schema alteration related issues fixes and tests backported from 1.1.x branch.

git-svn-id: http://svn.svnkit.com/repos/sqljet@1296 06c6b4df-3a75-4b2a-9d74-3e57e8079485
Table record modification in schema table was leaving duplicate records (both old and new).

git-svn-id: http://svn.svnkit.com/repos/sqljet@1297 06c6b4df-3a75-4b2a-9d74-3e57e8079485
Merged from trunk: table record modification in schema table was leaving duplicate records (both old and new).

git-svn-id: http://svn.svnkit.com/repos/sqljet@1298 06c6b4df-3a75-4b2a-9d74-3e57e8079485
Table record modification in schema table should update existing indices (not add new ones).

git-svn-id: http://svn.svnkit.com/repos/sqljet@1299 06c6b4df-3a75-4b2a-9d74-3e57e8079485
merged from trunk: table record modification in schema table should update existing indices (not add new ones).

git-svn-id: http://svn.svnkit.com/repos/sqljet@1300 06c6b4df-3a75-4b2a-9d74-3e57e8079485