l4test hang from CONFIG_X_PAGER_EXREGS

Hello,

I had some trouble with l4test, specifically it would hang during the 
IPC string test with page fault because a call to ExchangeRegisters (for 
aborting the IPC) failed.  I was able to get it to work by adding the 
following to my kernel/src/api/v4/exregs.cc file:

#define CONFIG_X_PAGER_EXREGS

 From reading the code it is fairly clear what this config does, but I 
did not see it anywhere as part of the "make menuconfig" for the kernel, 
so I had to add it manually.  I am not sure if this is something new or 
something on its way out, but I did want to let you know so you can 
either enable this by default or change the IPC test.

Cheers,
Sam