Previously, it just ran an Execute shell call with NULL as the command-line pointer.
The fix is to still call Execute, but with an empty string as the command line, and then check if the call gave an error. If running under plain GS/OS, this gives an error for an unknown system call, whereas both ORCA/APW and GNO shells will return with no error in this case. (Golden Gate doesn't implement the Execute shell call, so it also gives an error and will report no command processor available.)
This fixes issue #25.
These all behave identically to 'f'. Note that none of these accept the hexadecimal floating-point representation as input, which they should under C99.
'F' is currently treated identically to 'f'. This should be a correct implementation for 'F' under C99. (It's not quite correct for 'f', which should print "inf" or "nan" in lower case according to C99.)
'A' and 'a' are not correctly formatted (they are currently treated identically to 'E' and 'e', rather than using the hexadecimal floating-point representation specified by C99), but at least they print the number in some form and consume the correct number of bytes so that the stack isn't corrupted and subsequent conversion specifications print the right values.
The floating-point formats are also moved to the top of the list of conversion specifiers to check, which means they are checked last. This should marginally speed up the integer cases.
'z' corresponds to size_t, 't' to ptrdiff_t, and 'j' to intmax_t. In ORCA/C, these are all 32-bit types, so these size modifiers are equivalent to 'l'. (Note that C99/C11 require intmax_t to be at least 64-bit, but that is not currently the case in ORCA/C since there is no 64-bit integer type.)
The reverted changes relate mainly to adding a second character position in the putback buffer, but the library with those changes crashes on basic stdio operations like printing a string.
For now, this patch reverts stdio to a working, tested version. If the reverted changes are valuable, they can be fixed and then reintroduced later.
