tests/test-execute-bit.out

add documentation for revlog._prereadsize

adding a
79abf14474dc tip
% make sure we notice the change of mode if the cached size == -1
n   0         -1 unset               a
M a
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
d69afc33ff8a
not executable -- whew