Revert jl_errorf() to use vasprintf() rather than buf[1000].

Add comment for ios_write() call in jl_write() to explain why it is still required.

+    // This is needed because jl_printf() caller jl_static_show() in builtins.c can be
+    // called from fl_print in flisp/print.c (via cvalue_printdata()).
+    // cvalue_printdata() passes ios_t* to jl_static_show() for Historical reasons.

Replace one-and-only jl_puts() call in jl_static_show() with jl_printf()
for consistency.