Created new script to contain just functions that compare server versions

Add the new script to the db-core installer

Moved test for server-version comparers to their own script

Test script for just functions that compare server versions.

Move server-version comparers to own script

Fixes #230

Grudgingly used dynamic sql to execute CREATE INDEX IF NOT EXISTS so the script compiles with pre-pg9.5. Discarded the alternative of using just the pre-pg9.5 code for all versions to make sure the customization is easily found later.

The code to upgrade schema of table ConnectionActivity unnecessarily used IF NOT EXISTS. Removed this use and added comments to say why it is OK to remove IF NOT EXISTS.

Coincidentally, and fortunately, this change avoids having to execute pg-version specific code as required in Issue #230.

Using this edit as an opportunity to say:  Fixes #259

Had missed a couple more instances of Remove IF NOT EXISTS used with ADD COLUMN

Added gaurd for pg_event_trigger_ddl_commands() and updated testDDLActivityLogging.sql to support these changes

Guard CREATE INDEX IF NOT EXISTS for Postgres 9.4 or earlier

This reverts commit 9202699.

This reverts commit a1ad407.

Added triggers to prevent row deletion over tables DDLActivity and ConnectionActivity. The tables can still be truncated, still only by ClassDB role or a superuser.

Fixes #176

Also fixed a bug in the part that tested existence of triggers: used to test if at least one of the triggers are defined, instead of testing if all expected triggers are defined.

Updated the function logDDLActivity to not add values to DDLAcitivity for drop statements in versions  < 9.5. Also removed update to test scripts as they are now unneeded.

Reject row deletion over tables DDLActivity and ConnectionActivity

…_commands()

Guard uses of pg_event_trigger_ddl_commands() for Postgres 9.4 or earlier

These guards prevent any statements in enableConnectionLoggignReco.psql and disableConnectionLoggingReco.psql from being run if the current Postgres server version is < 9.4.

Use the pre-defined role pg_signal_backend only in server versions 9.6 or later. Fixes #225

Note: Depending on server version is technically not correct because the functionality in question is determined on the existence of a specific server role which can be tested in the pg_roles table. However, testing for server version is more practical and maintainable.

Use dynamic SQL to grant a role to CURRENT_USER in pg9.4 or earlier versions.

Fixes #229

Related to #229, but instead of guarding for  pg9.4 or earlier, reused the helper function ClassDB.grantRole. This keeps the test script simple and maintainable.

Must use dynamic SQL for all pg versions so the script compiles in pg versions 9.4 and earlier

Guard uses of ALTER SYSTEM for pg9.3 compatability

Use machine-readable version number to determine current server's version

Adds a temp function that when given a DROP OWNED BY query it will dynmically EXECUTE the query with an attach CURRENT_USER

Guard GRANT to CURRENT_USER in pg9.4 or earlier

initalizeServerCore.sql -> initializeServerCore.sql

Add Guard for DROP OWNED BY

Fix server initialization filename

Fix removeAllFromDB.sql

Added M4 docs to repo