GTK2: make sure string literals are 7 bit ASCII

clang has default encoding utf8 and will complain about non 7 bit chars
in string literals
block_alloc: removed just_find_*

This part of the old block allocator hash table api is not used anymore.
Removed one more non 7 bit string literal
Java: marked unused parameters to silence warnings
signal handling: UNUSED parameter is used in some cases
Pike.identify_cycle: Improved documentation somewhat.
Stdio.Stat: Survive casts to subtyped arrays (and mappings).

When casting an object to eg array(int), lfun::cast() gets the string
"array(int)". This used to cause Stdio.Stat::cast() to fail.
Interpreter: cast to unsigned before shifting to avoid signed overflow