':/<oneline prefix>' notation doesn't support full file syntax

Although the rev-parse documentation claims that the tree-ish:path/to/file syntax works is applicable, this is not so when using the :/ "oneline prefix" syntax:

% git rev-parse v1.5.0.1-227-g28a4d94 28a4d940443806412effa246ecc7768a21553ec7 % git rev-parse ":/object name" 28a4d940443806412effa246ecc7768a21553ec7

% git rev-parse v1.5.0.1-227-g28a4d94:sha1_name.c 0781477a71ac4d76a1b8783868d6649cae7f8507 % git rev-parse ":/object name":sha1_name.c :/object name:sha1_name.c fatal: ambiguous argument ':/object name:sha1_name.c': unknown revision or path not in the working tree. Use '--' to separate paths from revisions

A quick look at int sha1_name.c:get_sha1() shows that it doesn't even try to make this work. Is this worth fixing? Or at least documenting?

- Eric