Since `get-info/full` may return a function that is undefined
for the symbol 'scribblings, pass a failure thunk.
The function can be undefined for 'scribblings if:
1. Install a package with a `scribblings` in its info.rkt
2. Remove `scribblings` from the info file
3. Run `raco setup`
Along with the `PLT_COMPILED_FILE_CHECK` environment variable, allows
the timestamp check to be disabled when deciding whether to use a
compiled bytecode file.
In accomodating this change, `raco make` and `raco setup` in all modes
check whether the SHA1 hash of a module source matches the one
recorded in its ".dep" file, even if the timestamp on the bytecode
file is newer. (If the compile-file check mode is 'exists, the
timestamp is completely ignored.)
When custom categories are used in older versions, raco setup will
report a warning, but the documentation will still appear under the
Miscellaneous section. Thus, this is a backwards compatible
implementation of the idea.
On my machine, the sync path was sometimes triggered for "htdp-ptr".
(I'm not sure why; progress toward determinsitic bytecode might
be relevant.) Adjust the trigger for sync mode to check that the
needed "provides.sxref" file exists.
Rending a document can deserialize values, which can load modules
that would otherwise not be loaded by Scribble, so render each
document with a fresh namespace that is discarded after rendering.
