Why does rewriteAssetPath forbid trailing = (equals)?

The regular expression in `rewriteAssetPath()` forbids trailing equals, so this means if I have an asset key like `path/to/asset.png` this will successfully rewrite `path/to/asset.png?1234` but _not_ `path/to/asset.png?v=1234`.

My feeling is that it's a bug that the former is allowed but the latter is not, but I'm unsure as to whether they should both be allowed or forbidden,