add --json-error-messages (not yet implemented)

Added --json-error-messages option, which includes error messages in the
json output, rather than outputting them to stderr.

The actual rediretion of errors is not implemented yet, this is only
the docs and option plumbing.

This commit was supported by the NSF-funded DataLad project.

Command/FindRef.hs

@@ -12,7 +12,7 @@ import qualified Command.Find as Find
 import qualified Git
 
 cmd :: Command
-cmd = withGlobalOptions nonWorkTreeMatchingOptions $ Find.mkCommand $ 
+cmd = withGlobalOptions [nonWorkTreeMatchingOptions] $ Find.mkCommand $ 
 	command "findref" SectionPlumbing
 		"lists files in a git ref"
 		paramRef (seek <$$> Find.optParser)