HPCC-11213 Allow roxie queries with ambiguous elements

Some existing applications migrating to OSS relied on this
undesirable behavior.

Add optional PTree support for not throwing and exception when querying
properties with ambiguous xpaths.  Make it optional by requiring the
flag ipt_allowAmbiguousXpath when creating the PTree.

Add optional roxie support for queries with ambiguous elements.  Make
it configurable using the config option allowAmbiguousRequests.

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>