merge: when current branch has 1 or > 2 heads, actually abort.
Currently merge just prints abort-like messages to stderr and then
exits with a misleading status 0 (cleverly disguised as "False").
With this change it raises Abort, just like every other fatal error.
*** Test in-uri schemes
CFG: {x.prefix: http://example.org}
URI: http://example.org/foo
('x', 'x')
URI: http://example.org/foo/bar
('x', 'x')
URI: http://example.org/bar
('x', 'x')
URI: https://example.org/foo
abort
URI: https://example.org/foo/bar
abort
URI: https://example.org/bar
abort
CFG: {x.prefix: https://example.org}
URI: http://example.org/foo
abort
URI: http://example.org/foo/bar
abort
URI: http://example.org/bar
abort
URI: https://example.org/foo
('x', 'x')
URI: https://example.org/foo/bar
('x', 'x')
URI: https://example.org/bar
('x', 'x')
CFG: {x.prefix: http://example.org, x.schemes: https}
URI: http://example.org/foo
('x', 'x')
URI: http://example.org/foo/bar
('x', 'x')
URI: http://example.org/bar
('x', 'x')
URI: https://example.org/foo
abort
URI: https://example.org/foo/bar
abort
URI: https://example.org/bar
abort
CFG: {x.prefix: https://example.org, x.schemes: http}
URI: http://example.org/foo
abort
URI: http://example.org/foo/bar
abort
URI: http://example.org/bar
abort
URI: https://example.org/foo
('x', 'x')
URI: https://example.org/foo/bar
('x', 'x')
URI: https://example.org/bar
('x', 'x')
*** Test separately configured schemes
CFG: {x.prefix: example.org, x.schemes: http}
URI: http://example.org/foo
('x', 'x')
URI: http://example.org/foo/bar
('x', 'x')
URI: http://example.org/bar
('x', 'x')
URI: https://example.org/foo
abort
URI: https://example.org/foo/bar
abort
URI: https://example.org/bar
abort
CFG: {x.prefix: example.org, x.schemes: https}
URI: http://example.org/foo
abort
URI: http://example.org/foo/bar
abort
URI: http://example.org/bar
abort
URI: https://example.org/foo
('x', 'x')
URI: https://example.org/foo/bar
('x', 'x')
URI: https://example.org/bar
('x', 'x')
CFG: {x.prefix: example.org, x.schemes: http https}
URI: http://example.org/foo
('x', 'x')
URI: http://example.org/foo/bar
('x', 'x')
URI: http://example.org/bar
('x', 'x')
URI: https://example.org/foo
('x', 'x')
URI: https://example.org/foo/bar
('x', 'x')
URI: https://example.org/bar
('x', 'x')
*** Test prefix matching
CFG: {x.prefix: http://example.org/foo, y.prefix: http://example.org/bar}
URI: http://example.org/foo
('x', 'x')
URI: http://example.org/foo/bar
('x', 'x')
URI: http://example.org/bar
('y', 'y')
URI: https://example.org/foo
abort
URI: https://example.org/foo/bar
abort
URI: https://example.org/bar
abort
CFG: {x.prefix: http://example.org/foo, y.prefix: http://example.org/foo/bar}
URI: http://example.org/foo
('x', 'x')
URI: http://example.org/foo/bar
('y', 'y')
URI: http://example.org/bar
abort
URI: https://example.org/foo
abort
URI: https://example.org/foo/bar
abort
URI: https://example.org/bar
abort
CFG: {x.prefix: *, y.prefix: https://example.org/bar}
URI: http://example.org/foo
abort
URI: http://example.org/foo/bar
abort
URI: http://example.org/bar
abort
URI: https://example.org/foo
('x', 'x')
URI: https://example.org/foo/bar
('x', 'x')
URI: https://example.org/bar
('y', 'y')