class library: loadRelative permits access to switch warning on or off
class library: add an action to be called when loading paths
class library: removing obsolete argument in Environment:linkDoc.
When linking a document to an environment, now document itself takes responibility for pushing it.
help: document linkDoc and unlinkDoc methods
class library: linking a document and an environment now works correctly.
Also removing an environment from a document by setting its envir instavr to nil correctly restores the old environment.
help: Pdef/Pdefn function examples
class library: add space after error messages to separate them from each other.
class library: curvelin is now a proper inverse of lincurve (fix by james harkins).