Indicate hooked loading in load-verbose output

This is for troubleshooting.  If load-hook feature is used while loading
a file, the output of load-verbose is indicated by "(hooked)" to show
it's not a normal load.  The message can be refined in future to show
the real source (e.g. in-memory, from archive, etc.)
Some more support for static linking

Added gauche/static.h for the convenience of apps to link
static version of libgauche.

The static version of library is now named as libgauche-static-X.Y.a,
so that it'll be easier to link it to an app, while leaving other libraries
to be dynamically linked.