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You can try to use the PL/SQL TextMate bundle you can find at http://code.google.com/p/oracle-textmate-bundle/

How you can install TextMate bundles is explained in the manual.
Sorry, but that is no real solution. I'm sure there are people who want to enter these characters - especially if you think globally. Also, each international keyboard has different character mappings. So while a certain key combination yields "œ" on an US keyboard, it will map to a different character on a German or French keyboard - let alone Japanese or Chinese. There is no way to determine which keyboard the user has activated so this won't work.
No, sorry, I'm using APIs that are only available in iOS 5. Due to changes in Core Animation it also makes testing a lot easier. I also have not found that iOS 5 slows down the first generation iPad.
It's possible using private APIs. I don't want to risk my app being rejected by Apple.
Textastic can load TextMate-compatible syntax definitions - this is described in the manual.

Unfortunately with a quick search I couldn't find a TextMate bundle for the language you mentioned.
Unfortunately, there's no API for that. See http://feedback.textasticapp.com/topic/20131-better-hardware-keyboard-support/
Sounds like an interesting idea. I'll try it out when I have some time.
You should already be able to see them. For FTP connections, you need to enable the "Show hidden files" option in the FTP connection's settings. You can edit the connection's settings by tapping on the blue arrow on the right side of the connection.
I'm considering adding Multimarkdown preview support in the future.