If autocommit is set to false, read only will be set on begin
transaction.
If autocommit is true, it will continue to be managed at session level.
The queries to change session have been cached to avoid re-parsing each
time readonly value changes.

pgjdbc#1228
pgjdbc#848

checkstyle and hamcrest test import

add connection property with 3 options to control read only behavior

fix missing property methods on BaseDataSource
avoid redundant static modifier

more loosely couple read only hints to backend

return default read only mode from data source.

avoid case conversion

# Conflicts:
#	pgjdbc/src/main/java/org/postgresql/core/v3/QueryExecutorImpl.java
#	pgjdbc/src/main/java/org/postgresql/jdbc/PgConnection.java

# Conflicts:
#	pgjdbc/src/main/java/org/postgresql/core/v3/QueryExecutorImpl.java