Enhance the sqlite3_load_extension() so that when the entry point is

Enhance the sqlite3_load_extension() so that when the entry point is
not specified, after trying sqlite3_extension_init() and
sqlite3_X_init() where X is the alphabetic part of the base filename,
if neither or found it tries again with X as the alpha*numeric* part
of the base filename.  Hence, a shared library named "vt02.so" can be
loaded with just ".load vt02" and without having to specify the entry
point separately.

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