[TIMOB-2335] iOS: Filesystem method spaceAvailable should return bytes available instead of a boolean [API SCRUB]

ENVIRONMENT:

[From titanium_mobile/dist/os x/…/version.txt] version=1.5.0
timestamp=11/12/10 10:37
githash=937631f

STEPS TO REPRODUCE:
1) Pull down the latest titanium_mobile from github
2) Note …/apidoc/ File.tdoc says:
spaceAvailable: return boolean to indicate if the path has space available for storage
3) Note implementation (code in TiFilesystemProxy.m) returns TRUE if space available, FALSE if not

SUGGESTED FIX:
Return an integer (unsigned, 64-bit?) that shows the number of bytes available; use 0 for none.
(Easy to do per code, and the android 2.0 tdoc apparently already says this: platform deviation?)

ISSUES:
• How to sync up with Android folks on the new "spec" created from comparing iOS and Android "realities"
• Thomas helped me write this per QA "Best Practices" but RFC is always welcome on how to improve the first of many LH tickets
(Request for Comments)

ISSUES:

I don't have Lighthouse permissions / access to set "Who's responsible"