revlog: change accesses to index entry elements to use positive offsets

revlog: parse revlogv0 indexes into v1 internally This lets us eliminate lots of special case code in our performance-sensitive index accessors.

revlog: only allow lazy parsing with revlogng files This will allow us to store indices in memory in a single entry format

revlog: simplify the v1 immediate parser - read all the data at once (large files are handled by the lazy parser) - cache the entire file for inline revlogs - simplify looping

revlog: set the threshold for lazy parsing higher A typical machine can parse a 1MB index in well under a second

revlog: simplify the v0 parser

revlog: add revlogio interface This lets us separate the logic for different on-disk revlog formats from the main revlog logic.

revlog: regroup parsing code

transactions: avoid late tear-down (issue641) We use weak references (ugh) to avoid having to manually delete transaction references out of each call frame when an exception occurs.

hgk: enable mouse wheel under Windows. For some reason, MouseWheel events are not routed under windows even in latest ActiveTcl 8.4.15 while they are under linux and macosx. These events are activated using code supplied with Tcl Tip 171: <http://www.tcl.tk/cgi-bin/tct/tip/171.html>. Strangely, the Tip code almost work but generates some unexpected infinite loop which is fixed using a simple boolean to check reentrancy.