#241 add support for dtx files

[Matthias Pospiech]

The 'tex' postfix is not the only file format valid in the tex-world. Especially the dtx format, which is used for the package documentations is very common.
Unfortunately texstudio is unable to handle these files.

1. they should be treated as normal tex files and scanned and highlighted
2. the highlighting rules must be different, since % is not a comment char anymore
3. the command for pdflatex add '.tex' which is wrong in this case. These however is a more general problem, since the commands can not be set project specific.

[Benito van der Zander]

1. the command for pdflatex add '.tex' which is wrong in this case. These however is a more general problem, since the commands can not be set project specific.

That's not a problem, although the default commands may be wrong.
The filename shouldn't be %.tex or ?m.tex, but "?ame" or ?me which will add the file extension of the master file.

[Tim Hoffmann]

dtx support added in rev. 2783.