implement the rest of the breakpoint test.

finally. seems to work. periodic strange bug where the breakpoint is
never hit, yet the program's output clearly indicates it got
through the break location.  we must be calculating the address
incorrectly... but only sometimes?
fix bug setting breakpoint.

we want to make sure we only overwrite the start of the
instruction, otherwise we can cause Bad Things(tm).  Also, the
length of the instruction is always one byte, by definition.
add an option to note/find every malloc in the program.