[pgjdbc/pgjdbc] 6ce917: fix: allow disabling field metadata cache(#1052)

Branch: refs/heads/master
  Home:   https://github.com/pgjdbc/pgjdbc
  Commit: 6ce91721048dea0e73231fa50c365108e9b9d49d
      https://github.com/pgjdbc/pgjdbc/commit/6ce91721048dea0e73231fa50c365108e9b9d49d
  Author: Marc Slemko <marcs@znep.com>
  Date:   2018-05-09 (Wed, 09 May 2018)

  Changed paths:
    M pgjdbc/src/main/java/org/postgresql/PGProperty.java
    M pgjdbc/src/main/java/org/postgresql/jdbc/PgResultSetMetaData.java
    A pgjdbc/src/main/java/org/postgresql/util/Gettable.java
    A pgjdbc/src/main/java/org/postgresql/util/GettableHashMap.java
    M pgjdbc/src/main/java/org/postgresql/util/LruCache.java
    M pgjdbc/src/test/java/org/postgresql/test/jdbc2/ResultSetMetaDataTest.java

  Log Message:
  -----------
  fix: allow disabling field metadata cache (#1052)

Clients accessing very dynamic schemas can have issues with the
field metadata cache getting stale.  This change allows configuring the
databaseMetadataCacheFields property to 0 to disable the cache and
avoid these issues where necessary.  This behaviour was already
documented, however did not actually work as the codepath assumed
it could retrieve the fields from the cache.



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