Added InvariantCulture to NpgsqlCopySerializer

PostgreSQL currently only supports SQL notation for decimal point (which
is the same as InvariantCulture)
Added static readonly CultureInfo field for use in string.Format to
always use dot as decimal point.
NpgsqlError

Fix bug that would cause NpgsqlError to stop reading error fields prematurally if it encountered a field type it doesn't understand.
NpgsqlError

Use enum for error message field codes.
Restructure the message reader so the null terminator is handled in a more obvious way.
Merge pull request #99 from glenebob/npgsql_error

NpgsqlError fix and improvement
Add test for #92
Merge pull request #1 from franciscojunior/add-test-for-pr92

Add test for pr92
Merge pull request #92 from djsubzero/master

Added InvariantCulture to NpgsqlCopySerializer
Ignore InvariantCultureNpgsqlCopySerializer test when running under protocol version 2

The test created by #92 hangs when running under protocol 2. It seems NpgsqlCopySerializer has a problem with this protocol version.
Ignored for while when running under protocol 2 until we verify why this is happening.
Merge pull request #103 from franciscojunior/ignore-copyserializer-test-from-pr92-protocol-2

Ignore InvariantCultureNpgsqlCopySerializer test when running under prot...