fix some "\n"-related stuff

add missing "\n"s to some Printf()-like calls (in Rend2)
drop erroneous "\n"s from some Error()-like calls (in Rend2)
drop erroneous "\n" from a Com_Error() call (in vm_sparc.c)
add some noreturn annotations
remove some redundant exit() calls
remove some unused stuff
make the fread() success-check code in Sys_RandomBytes() more secure
when using the condump command, do not say "dumped console text" prematurely, before trying to open the file
reduce the amount of compiler warnings for variable shadowing
drop some useless return statements
clean up return statements a bit more
fix some OOB enumerator usages

(should be no-op with usual compiler workings)