* :save takes a path and saves the current message part to that location
* :pipe is the same as pipe on the account page, but uses the current
message part rather than the whole email (ie :pipe gzip -d)
* Refactored account:pipe and extracted common pipe code to
commands.util.QuickTerm
* Added helper command aerc.PushError
Many Drawable implementations have their own Invalidate and OnInvalidate
functions, with an unexported onInvalidate field. However OnInvalidate and
Invalidate are usually not called in the same goroutine. This results in a race
on this field, e.g.:
Read at 0x00c000094748 by goroutine 7:
git.sr.ht/~sircmpwn/aerc2/widgets.NewDirectoryList.func1()
/home/simon/src/aerc2/widgets/dirlist.go:85 +0x56
git.sr.ht/~sircmpwn/aerc2/widgets.(*Spinner).Start.func1()
/home/simon/src/aerc2/widgets/spinner.go:93 +0x1bb
Previous write at 0x00c000094748 by main goroutine:
[failed to restore the stack]
Goroutine 7 (running) created at:
git.sr.ht/~sircmpwn/aerc2/widgets.(*Spinner).Start()
/home/simon/src/aerc2/widgets/spinner.go:46 +0x8f
git.sr.ht/~sircmpwn/aerc2/widgets.NewDirectoryList()
/home/simon/src/aerc2/widgets/dirlist.go:37 +0x286
git.sr.ht/~sircmpwn/aerc2/widgets.NewAccountView()
/home/simon/src/aerc2/widgets/account.go:50 +0x5ca
git.sr.ht/~sircmpwn/aerc2/widgets.NewAerc()
/home/simon/src/aerc2/widgets/aerc.go:60 +0x800
main.main()
/home/simon/src/aerc2/aerc.go:65 +0x33e
To fix this, introduce a new type, Invalidatable, which protects the field.
Unfortunately the Drawable must be passed to the callback function in
Invalidate, so we still need to re-implement this in each Invalidatable user.
