mesa: new _NEW_PROGRAM_CONSTANTS flag

mesa: new _NEW_PROGRAM_CONSTANTS flag

This state flag will be used to indicate that vertex/fragment program
constants have changed.  _NEW_PROGRAM will be used to indicate changes
to the vertex/fragment shader itself, or misc related state.

_NEW_PROGRAM_CONSTANTS is also set whenever a program parameter that's
tracking GL state has changed.  For example, if the projection matrix is
in the parameter list, calling glFrustum() will cause _NEW_PROGRAM_CONSTANTS
to be set.  This will let to remove the need for dynamic state atoms in
some drivers.

For now, we still set _NEW_PROGRAM in all the places we used to.  We'll no
longer set _NEW_PROGRAM in glUniform() after drivers/etc have been updated.