Adapt to core API changes

[laurenz]

• PostgreSQL commit 8237f27b504ff1d1e2da7ae4c81a7f72ea0e0e3e This v11 commit removed "get_relid_attribute_name", the replacement is "get_attname" with a third argument "false".

• PostgreSQL commit 9fa6f00b1308dd10da4eca2f31ccbfc7b35bb461 This v11 commit removed the individual size parameters for AllocSetContextCreate (which is now a macro) and foced usage of the ALLOCSET_DEFAULT_SIZES macro (which in turn did not exist before 9.6).

• PostgreSQL commit c6293249dc178f52dd508c3e6ff353af41c90b58 This v11 commit changed the internal representation of a tuple descriptor. You now have to use the "TupleDescAttr" macro to access the individual attributes.

In passing, add a ".gitignore" file.

[jenkins-juliogonzalez]

Can one of the admins verify this patch?

[GeoffMontee]

Test this, please

[jenkins-juliogonzalez]

Test PASSed.

[GeoffMontee]

Thanks for the patch!