Depend on Devel::CallChecker, use it on build time
Define LINKLIST and op_linklist if they are missing
Minor doc tweaks
Fixing tests to work on older perl versions
Test delaying looking into ${^GLOBAL_PHASE}
Skip doing a test on unsupported behavior
Teach Lazy.xs about the : pseudo-prototype.

Turns out that it is possible to combine the & prototype with
lazy arguments to get a pretty nifty map-style fucntion, which can
take either a block or an expression. The : proto makes this even
more convenient.