Correct limit on immediate operands
intval loading example(s)
Use intval_high_bit() for values
Correct asserts for loading unsigned ints that aren't longs

0x80000000 is an unsigned int, whose max bit is 31. This qualifies it
for (on certain architectures - Darwin) movabsq, but not for
interpretation as a long, so a distinction needs to be made.
Comment on backend sign extension
UCC_SZ_* type limits
intval truncation optimisation using native casting
Casting only needs in-size and signed information
Correct sign extension for compile-time signed casts
Added -f[no-]cast-with-builtin-types for testing bit casting
Allow negatives through 64-bit loads (fixes various failing bitfield tests)
Allow enums, etc through 64-bit loads for now

Will be fixed on the enum branch
Also updated test to check asm output
Fixed -ftrapv test
Fixed large-global test
Fixed type_ref_get_type() for typedefs
Refined array bound test
Put truncation/integer-conversion warnings for implicit casts back in
Backend truncation test - needs sorting