* For readability, rewrote ResourceLoaderFileModule::readScriptFiles() to use a loop instead of an excessively cute nested array_map() construction.
* In ResourceLoaderFileModule, check file_get_contents() result for errors. Golden rule of error checking: always check fopen(). Every call to fopen will fail some day for some user.
* In mediaWiki.loader.filter(): broke up a complex multi-line conditional into multiple commented if statements, for readability.
* Possessive "its" has no apostrophe.
* Modified Xml::encodeJsVar() to allow it to pass through JS expressions without encoding, using a special object.
* In ResourceLoader::makeModuleResponse(), renamed $messages to $messagesBlob to make it clear that it's JSON-encoded, not an array.
* Fixed MessageBlobStore to store {} for an empty message array instead of [].
* In ResourceLoader::makeMessageSetScript(), fixed call to non-existent function mediaWiki.msg.set.
* For security, changed the calling convention of makeMessageSetScript() and makeLoaderImplementScript() to require explicit object construction of XmlJsCode() before interpreting their input as JS code.
* Documented several ResourceLoader static functions.
* In ResourceLoaderWikiModule, for readability, reduced the indenting level by flipping some if blocks and adding continue statements.
* In makeCustomLoaderScript(), allow non-numeric $version. The only caller I can find is already sending a non-numeric $version, presumably it was broken. Luckily there aren't any loader scripts in existence, I had to make one to test it.
* wfGetDb -> wfGetDB
* Added an extra line break in the startup module output, for readability.
* In ResourceLoaderStartUpModule::getModuleRegistrations(), fixed another assignment expression
