I've fixed a tiny bug in RefTeX: TOC was not shown for dtx files.

Dtx files mix code and documentation. Any comment with the comment 
character at the beginning of the line is considered a part of the docs.

The regexp gathering sections allowed only whitespace before the section 
command. I've changed this so that now, the comment character is also 
allowed at the very beginning. In the parser code, I've added a filter 
that accepts only commented lines for dtx files and only uncommented 
ones for other files.

I've relied on the file name (ending in ".dtx", obviously), to detect 
dtx files. Using the major mode (doctex-mode or not) of the file that is 
currently visited does not work, as a tex file can input a dtx file, or 
vice versa. Maybe there's a way to also check file variables of included 
files, but I don't know about it, and it would probably be an overkill, 
anyway.

Best,
Sašo