Fix a build error in Bikeshed

[romandev]

This fixes #2460.

[romandev]

@tabatkins, @foolip PTAL

[foolip]

Does this fix the problem? Odd :)

[tabatkins]

Hm, this shouldn't be necessary - I thought I allowed single-line pre just fine. (When it is multiline, I do purposely only allow the start/end tag by themselves on their line, with the content on intervening lines.) I'll look into it.

[tabatkins]

Oh, I see the problem! Since I look for data-blocks before HTML parsing (so they can include things that would make HTML unhappy), I do a really minimal parse to figure out what things are.

In particular, this build error is caused by me finding that the line starts with <pre, and then seeing that it includes the substring include, which classifies it as an include-block rather than an ordinary pre. :(

I should bite the bullet and actually do a little bit of real parsing of the tag; that bit of the HTML parser isn't complicated.

[tabatkins]

The build error has been fixed on Bikeshed' side, so closing this.