#29 Unifying #include style

[Harri Porten]

I noticed that the #include statements used in BLT
files are not consistent. While most blt*.h files are
included using "..." some are included with the <....>
syntax. This leads to problems when another BLT
installation is in the include path first or if -I. is
not set.
I therefore suggest to change the few #include <blt*.h>
statements to #include "blt*.h". I have attached a
patch which does that for the last remaining ones I
still had in my local copy. There were more iirc.

[Harri Porten]