ngIRCd Release 21~rc1
ngircd.c, main(): use strlcat() instead of strcat()

This fixes the following warning on OpenBSD 5.3:

 ngircd.o(.text+0xeb4): In function `main':
  src/ngircd/ngircd.c:300: warning: strcat() is almost always misused,
                                    please use strlcat()

Thanks to Götz Hoffart for reporting this!
Fix spelling in NEWS and ChangeLog files
INSTALL file: Update "Upgrade Information"
ChnageLog file: even more spelling fixes ...
Update (date of) manual pages
platformtest.sh: Detect Apple LLVM (clang) compiler
platformtest.sh: Clean up GIT source tree, when possible