Tolerate JSlint

COUCHDB-561

The only errors left are:
```
./node_modules/jslint/bin/jslint.js --maxerr=100 jquery.couch.js                                                                                                *[master] [17:22:19] ▸▸▸▸▸▸▸▸▸▸

jquery.couch.js
 #1 Unexpected TODO comment.
    // todo: can we use commonjs require here? // Line 312, Pos 13
 #2 Unexpected 'typeof'. Use '===' to compare directly with undefined.
    if (typeof Base64 === "undefined") { // Line 313, Pos 15
 #3 Expected exactly one space between 'return' and '{'.
    return /** @lends $.couch.db */ { // Line 326, Pos 39
 #4 Unnecessary 'else' after disruption.
    } else { // Line 618, Pos 13
 #5 Unused '_'.
    function (_, doc) { // Line 781, Pos 23
 #6 Unused 'ajax'.
    function ajax(obj, options, errorMessage, ajaxOptions) { // Line 1081, Pos 12
 #7 Unused 'fullCommit'.
    function fullCommit(options) { // Line 1154, Pos 12
 #8 Unused 'encodeOptions'.
    function encodeOptions(options) { // Line 1171, Pos 12
 #9 Unused 'toJSON'.
    function toJSON(obj) { // Line 1194, Pos 12
#10 Unused 'maybeUseCache'.
    function maybeUseCache() { // Line 1201, Pos 12
```

Unused are happens because of globals workaround; TODO remains TODO; typeof have to compare with undefined since Base64 is a browser's global thing; else is better to keep for readability.