Improve error logged when there's an exception applying ops

[nickbrowne]

We're still getting intermittent "Deleted string does not match" errors despite some of the other fixes applied, hoping that just logging the strings attempted to be deleted will reveal the problem.

To test (assuming starting from a blank slate):

npm install && npm run build
createdb sharejs_example
bin/sharejs

Now we need to create a json type document with a text type subdocument, insert a string, then give it a bad delete op:

Create a document
curl -X PUT -H 'Content-Type: application/json' -d '{"type": "json"}' http://localhost:9000/doc/test

Post an object insert op to insert an empty object to create a json document type
curl -X POST -H 'Content-Type: application/json' -d '[{ "p": [], "oi": {} }]' http://localhost:9000/doc/test?v=0

Object insert on the key "test", inserting an empty string to create a text subdocument within the json document
curl -X POST -H 'Content-Type: application/json' -d '[{ "p": ["test"], "oi": "" }]' http://localhost:9000/doc/test?v=1

String insert on the text subdocument
curl -X POST -H 'Content-Type: application/json' -d '[{ "p": ["test", 0], "si": "foo bar" }]' http://localhost:9000/doc/test?v=2

At this point do a GET on the document just to sanity check it's as expected:
curl http://localhost:9000/doc/test

Should return
{"test":"foo bar"}

Now give it a bad delete operation to trigger the exception.

We want to delete from the last 'o' in foo to the 'a' in bar to send up with "for", but give it some bogus delete text
curl -X POST -H 'Content-Type: application/json' -d '[{ "p": ["test", 2], "sd": "xxxx" }]' http://localhost:9000/doc/test?v=3

This should raise an error
test Error: Deleted string does not match (1: "o ba" 2: "xxxx")

Now give it a properly formed delete op
curl -X POST -H 'Content-Type: application/json' -d '[{ "p": ["test", 2], "sd": "o ba" }]' http://localhost:9000/doc/test?v=3

GET the document again
curl http://localhost:9000/doc/test

The subdocument should only contain "for"
{"test":"for"}

[RohanM]

Nice 🚀