export_measures implicitly converts number-like data, resulting in bad 0-lead labels

[shippy]

This is a problem for youthreport_shq1 and youthreport_shq3, which are coded like so:

code	label
1800	6:00p.m.
1830	6:30p.m.
1900	7:00p.m.
1930	7:30p.m.
2000	8:00p.m.
2030	8:30p.m.
2100	9:00p.m.
2130	9:30p.m.
2200	10:00p.m.
2230	10:30p.m.
2300	11:00p.m
2330	11:30p.m.
0000	12:00a.m.
0030	12:30a.m.
0100	1:00a.m.
...	...

Instead of 0000, we export 0. Instead of 0030, we export 30. While this can be worked around, it is contrary to the data dictionary we publish.