Assorted code cleanups

• Clear up -Wcast-function-type warnings from NotImplemented()
• Remove unused empty NoopDDA() function
• Remove unused EventSwap functions & dispatch vector
• DetachStdio: check that open & dup2 functions succeed
• Remove no-op OsInitAllocator()
• Avoid memory leak if -ls specified multiple times on command line
• Add FSallocarray for array allocation with overflow check
• Make FScalloc take two args like standard calloc
• Replace alloc+bzero pairs with FScalloc calls
• Replace obsolete bzero call with standard memset call
• Add FSreallocarray for array reallocation with overflow check
• Get rid of fsalloc/fsrealloc/fsfree wrapper macros
• print error messages if syslog support is built but disabled
• Mark FatalError as _X_NORETURN
• Add alloc_size & malloc attributes to allocation functions
• QueryExtents: Avoid memory leak in error path
• QueryBitmaps: Avoid memory leak in error path
• SetFontCatalogue: handle allocation failure
• WriteToClient: handle allocation failure