Fix the use of a multi-level object key (e.g. foo.bar) as the key for an index lookup inside non-self-closing tags.

Closes #521.

This internal `.text` property is used to compare start and close tags to ensure they're balanced. When the tag contains a path lookup, the lookup is itself a compiled node. When a node is compiled, line-number information is attached, which causes the tag to become inbalanced.

The patch simply strips line-number information from this internal marker.
As we discussed in the meeting today this gets scary when people have variables named "line"