* Push/pop environment to make sure it is isolated from our parents and children.
* Make all environment vars (and shell vars) case-insensitive, consistent with GNO's internal handling of environment vars.
* Wrap putenv and unsetenv to make sure they are called with lower-case variable names, which is necessary to maintain consistency between the environ array and the kernel's internal representation of variables.
*Use .null instead of /dev/null
*Account for GNO's dup2(), which non-standardly returns 0 on success
*Always call open with appropriate number of arguments
*Use STDIN_FILENO instead of (implicitly) 0
This code could theoretically break if the ORCA/C varargs implementation changed, but it should be OK in practice.
Also removed some unused code in libbb/xfuncs.printf.c that includes potentially problematic varargs use (defining varargs functions but not necessarily calling va_start/va_end in them).
Dmake gets confused if you use over-15-character file names, so they needed to be shortened to get it to work. While I was at it, I also switched _ to . in the filenames so they're fully ProDOS compatible.
The shell/hush_test directory (not needed to build the code) still uses ProDOS-incompatible file names.
Stephen Heumann