load extensions only after the ui object has been completely initialized
This fixes a traceback printed when hg tries to print another traceback
after an extension fails to be loaded. Add a test for that.
#!/bin/sh
echo % init
hg init
echo % commit
echo 'a' > a
hg ci -A -m test -u nobody -d '1 0'
echo % annotate -c
hg annotate -c a
echo % annotate -d
hg annotate -d a
echo % annotate -n
hg annotate -n a
echo % annotate -u
hg annotate -u a
echo % annotate -cdnu
hg annotate -cdnu a