hashtable.c: do not rechain in lookup

Reordering the bucket list during lookup is very expensive. Removing it
makes cpp() about 10% faster on a file that only contains define and if
defined() statements.
Additionally, the const attribute on the hash table argument is correct now.
check_size_shift: added const
sprintf: update the local stack top pointer

When a call to low_pike_sprintf reallocates the format stack during
snurkel handling, the local stack pointer variable becomes invalid.
Update it after handling snurkels.
sslfile -> File and sslport -> port
Save all of 64 bytes.
SSL: Added support for the subjectAltName extension.
Precompiler: Make the program(s) in progress available.

When compiling subclasses it is sometimes needed to access stuff in the
parent program, so make it available as soon as it starts existing,
instead of only after it has finished compiling.