report sizes of js files during build

This modifies the <transform> ant task so that it reports the
sizes of its inputs and outputs. So when we capture ant build
output, we can pull out the js sizes and track it over time.

output looks like this:

[transform] input 1021 bytes from caja-iframe-build-version.js
[transform] input 781 bytes from createExports.js
[transform] input 66327 bytes from acorn.js
[transform] input 82047 bytes from escodegen.js
[transform] input 12080 bytes from estraverse.js
[transform] input 1145 bytes from exportsToSES.js
[transform] input 12400 bytes from mitigateGotchas.js
[transform] input 871 bytes from caja-iframe-done.js
[transform] building 8 files to ant-lib/com/google/caja/plugin/utility-frame.opt.js
[transform] output (javascript,minify) 93893 chars to utility-frame.opt.js
[transform] building 8 files to ant-lib/com/google/caja/plugin/utility-frame.js
[transform] output (concat) 176674 chars to utility-frame.js

[kpreid2, 2013-08-22 01:51:45]

LGTM

[felix8a, 2013-08-22 08:15:30]

@r5571