Special variables are used before being declared special

[pfdietz]

A number of special variables are being declared special in api.lisp (catch-errors, etc.). However, they are used before that file is loaded. This use is not standard compliant, and produces warnings under sbcl.

[joaotavora]

Indeed a point of improvement, if minor. Make a PR declaring them in some existing or new file loaded before common.lisp and submit here for discussion.