#22 Compile/Run against Tcl 8.6

[Jan Nijtmans]

Here are the changes to tclblend, which allow it to be compiled without
warnings against Tcl 8.4, 8.5 and 8.6. I didn't check whether some
of those changes are in CVS already, this are the modifications
against tclBlend 1.4.1.

The most important change is the return value of Tcl_GetObjType().
The 'hack' used by tclblend results in a compiler warning, but
a single type cast can silence this. The signature change
results in another warning, which can be resolved by making
listTypePtr a const pointer.

Additionally, added a few more internal 'const' decorations,
which reduce the number of warnings when compiling tclblend
with -Wwrite-strings.

Regards,
Jan Nijtmans

[Jan Nijtmans]

patch for Tcl 8.6