Fix use of tc-literal
fix magic-open-paren bug

also, replace some eq?s with equal?s.
Open Require Path: ignore .bak files under windows, but ~ files elsewhere

instead of ignoring ~ files everywhere
Handle methods that have opt args but no kws

Closes PR 14726
web pages: change "Source" to "Unix Source" for non-minimal source
plt-web: leave the `tt` font alone
download web pages: notes on source distributions

Closes 14694
JIT: fix problem with arity checking with >= 25 arguments
optimizer: move more things inside let and begin

Refactor the code to move inside 'let' or 'begin'.

Also, in the test position of a 'if', recognize the 'not' inside a 'let' or 'begin'.
For example, transform (if (begin ... (not p)) x y) => (if (begin ... p) y x)
Previously, this conversion was made only when
the 'not' was the outermost expression.

And use the refactored code to move application inside 'let' or 'begin' in a single step
For example, transform ((let (...) ... (let (...) ... f) x) => (let (...) ... (let (...) ... (f x))
In the conversion, it's necessary to shift x to the new coordinates inside the 'let's.
In the new version x is shifted only once.
add a test case for parametric->/c that tests that the
polymorphic variables are actually instantiated when the
function is called
improve parametric->/c's cooperation with a few bells and whistles in contract error reporting
Fix opt-lambda property on opt-lambda methods

Related to PR 14726