Merge version-2.2 & version-2.5 changes into master

[Schmed]

I tried doing this myself today, but abandoned the effort. A few notes:

• Adbeat (through 4.0) is currently using cascading.solr-2.2.4 (and solr-core-4.2.1), though I plan to try to apply my MD5 changes soon, and may release a 2.2.5 today.
• Adbeat 5.0 is currently using solr-core-8.2.0 and cascading.solr-2.6-SOLR8.
• cascading.solr-2.5 and cascading.solr-2.6-SNAPSHOT are currently using solr-core-4.10.1.
• Some changes have been cherry-picked from version-2.5 into version-2.2.

[Schmed]

You'd obviously want to merge the same changes from master into (at least) 13_update-solr8