use commit time as mtime for file archives.
now output from two run of "hg archive -t zip" is same.
1:016807e6fdaf
0:eb43f19ff115
016807e6fdaf tip
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
eb43f19ff115
eb43f19ff115+
reverting file1
? file1.orig
eb43f19ff115
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
? file1.orig
016807e6fdaf tip
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
merging file1
0 files updated, 1 files merged, 0 files removed, 0 files unresolved
? file1.orig
016807e6fdaf tip
? file1.orig
016807e6fdaf tip
? file1.orig
016807e6fdaf tip
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
? file1.orig
016807e6fdaf tip