[krbdev.mit.edu #3223] gss_acquire_cred should search for the desired client principal if possible

[Alexandra Ellwood via RT]

When passed GSS_C_INITIATE and a non-NULL desired name, gss_acquire_cred should 
search the available credentials caches rather than simply failing if tickets for the 
desired client principal are not in the default ccache.

Note: targeted for 1.4.3 so KfM and KfW can ship it sooner than 1.5.  Patches to fix 
this bug will not affect Unix platforms because currently they only have one file-based 
ccache at a time.