revlog: add revlogio interface
This lets us separate the logic for different on-disk revlog formats from
the main revlog logic.
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.
hgk: enable mouse wheel on MouseWheel events.
At this point, mouse wheel still does not work under Windows.