libbanshee also using a broken AC_HEADER_STDBOOL

[Paolo Bonzini]

> Although I defer judgement on autoconf/automake matters to you, I am
> perplexed why you wish to effectively substitute:

Because ACX_HEADER_STDBOOL formed the basis of the AC_HEADER_STDBOOL 
Autoconf 2.5x macro.  They incorporated a lot more consistency checks, 
and it seems worth to bring them back.

My macro additionally had a check for sizeof (bool) == 1 to ensure 
consistency between system.h's replacement bool and a bool declared in 
stdbool.h (this is for toplevel bootstrap, where you can run configure 
scripts under different compilers, which may have different sizeof(bool) 
values: we should ensure that only one is used).

Paolo