A subfont with n chars has n+1 Fontchars, so scalesubfont() needs to
scale all n+1 info entries.

The function `startrpc()` stack allocates a local buffer of size 100:

```c
static Muxrpc*
startrpc(int type)
{
	uchar buf[100];
	      ^^^^^^^^
	Wsysmsg w;

	w.type = type;
	convW2M(&w, buf, sizeof buf);
	return muxrpcstart(display->mux, buf);
}
```

The function `convW2M()` is called passing `buf`. That function accesses
`buf` out-of-bounds:

```c
uint
convW2M(Wsysmsg *m, uchar *p, uint n)
{
  ...
  case Tcursor2:
    PUT(p+6, m->cursor.offset.x);
    PUT(p+10, m->cursor.offset.y);
    memmove(p+14, m->cursor.clr, sizeof m->cursor.clr);
    memmove(p+46, m->cursor.set, sizeof m->cursor.set);
    PUT(p+78, m->cursor2.offset.x);
    PUT(p+82, m->cursor2.offset.y);
    memmove(p+86, m->cursor2.clr, sizeof m->cursor2.clr);
    memmove(p+214, m->cursor2.set, sizeof m->cursor2.set);
    p[342] = m->arrowcursor;
    ^^^^^^
```

To fix the issue the size of local variable `buf` is increased from 100
to 512 to avoid out-of-bounds array access.

Runes in Plan 9 were limited to the 16-bit BMP when I drew up
the RPC protocol between graphical programs and devdraw
a long time ago. Now that they can be 32-bit, use a 32-bit wire
encoding too. A new message number to avoid problems with
other clients (like 9fans.net/go).

Add keyboard shortcut alt : , for U+1F602, face with tears of joy,
to test that it all works.

This matches the Plan 9 behavior a bit better.

Fixes #30.

May fix a deadlock / missing font on OpenBSD.

Fixes #308.