win32 file locking

[Aaron Bentley]

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John A Meinel wrote:
| The problem is that Branch() is commonly used as a temporary object. For
| instance the 'bzr revno' command is done like:
|
| print Branch('.').revno()
|
| How do you unlock a branch if you never have an object to call
| 'unlock()' on?

How about this: only do permanent locks if we want them.  Basically, we
have a class NewBranch where almost every method is just a decorated
call to Branch:

class NewBranch:
...
~    def lock(type):
~        self.locked_branch = Branch(self.path, type)

~    def unlock()
~        self.locked_branch.unlock()
~        self.locked_branch = None

~    def revno():
~        if self.locked_branch is not None:
~            cur_branch = self.locked_branch
~        else:
~            cur_branch = Branch(self.path, type)

~        result = cur_branch.revno()
~        if cur_branch is not self.locked_branch:
~            cur_branch.unlock()

This way
1. We don't keep any state between method calls, aside from the branch path.
2. We can still do locking when we want to.

AIUI, auto-decorating every method in Branch is pretty easy in Python.

Aaron
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