[plt-scheme] project

When I have a Scheme program about thousand LOC opened in definition 
window and "reindent all", it takes quite a few seconds for DrScheme to 
indent, and DrScheme stops to react during this time. I haven't checked 
the code, but it seems the current code takes O(loc^2) time to "reindent 
all", although it can be done in O(loc) time.

 > The strategy is very simple: look backwards for '{'s. Count them.
 > Insert twice that number of spaces at the beginning of the line.
 > Unless the line's first character is '}', in which case, insert two
 > fewer spaces.

Chongkai