Deadlock with render_mutex and fifo_mutex

[Vort]

While watching how my GlideTest_v3.zip program spins triangle (Windows 95 + Voodoo 3), I noticed Bochs hang. This most likely happens as side effect of #264 fix. Hang is random because it is caused by race condition.

It is possible to get deadlock with render_mutex and fifo_mutex. Here are stack traces:

Main thread:

>	bochs.exe!bx_voodoo_base_c::update() Line 575	C++
 	bochs.exe!bx_banshee_c::update() Line 971	C++
 	bochs.exe!bx_vgacore_c::vga_timer_handler(void * this_ptr) Line 2410	C++
 	bochs.exe!bx_virt_timer_c::periodic(unsigned __int64 time_passed, bool mode) Line 149	C++
 	bochs.exe!bx_virt_timer_c::timer_handler(bool mode) Line 435	C++
 	bochs.exe!bx_pc_system_c::countdownEvent() Line 382	C++
 	[Inline Frame] bochs.exe!bx_pc_system_c::tickn(unsigned int n) Line 115	C++
 	bochs.exe!BX_CPU_C::cpu_loop() Line 123	C++
 	bochs.exe!bx_begin_simulation(int argc, char * * argv) Line 1051	C++
 	bochs.exe!win32_ci_callback(void * userdata, ci_command_t command) Line 798	C++
 	bochs.exe!bx_real_sim_c::configuration_interface(const char * ignore, ci_command_t command) Line 940	C++
 	bochs.exe!bxmain() Line 337	C++

FIFO thread:

>	bochs.exe!swap_buffers(_voodoo_state * v) Line 1135	C++
 	bochs.exe!swapbuffer(_voodoo_state * v, unsigned int data) Line 1162	C++
 	bochs.exe!register_w(unsigned int offset, unsigned int data, bool log) Line 2101	C++
 	bochs.exe!cmdfifo_process(_cmdfifo_info * f) Line 3139	C++
 	bochs.exe!fifo_thread(void * indata) Line 235	C++

1. Main thread: bx_voodoo_base_c::update locks render_mutex;
2. FIFO thread: swapbuffer locks fifo_mutex;
3. Main thread: bx_voodoo_base_c::update locks fifo_mutex;
4. FIFO thread: swap_buffers locks render_mutex.

Version: 35e9350