Changed paths and the rule for checking.
Removed redundant checks and fixed an assert statement.
Converted tabs to spaces for consistency.
Removed print_matrix function.

This function was needed only for debugging (and violates
the guidelines for R extensions: don't write to stdout).
Added inline documentation

for constant.vars and inverse.gnomonic.  Also simplified
the function distances somewhat.
Improved Makefile.
Exported inverse.gnomonic and constant.vars.

Also added useDynLib declarations.
Removed Rd files.

These are automatically generated and don't need to be tracked.