Improve messages from shell's upgradeCheck() methods.

a few things to improve:

• print error message then doc rather then full sentence which is hard to read
  change db and collection checks to give a return message in standalone
• “Invalid index spec for <index name>: <index spec>”
• start lines with “Document|Index|Collection Error: <desc> (if needed : <target>)”
• when index too large, print spec as well “Key for index <index name> (<spec>) too long on following document: <doc>”