Fix samples/rot13_concise + libxml compilation error

boehm_gc/.gitignore:
    Ignore .obj files

extras/xml/xml.dtd.m:
extras/xml/xml.parse.m:
    Change the name of functor ('1') in the multiplicity/0 type
    to one. The former name does not (yet) work with the C# grade.

samples/.gitignore:
    Ignore library output and sample executables.

samples/c_interface/standalone_c/.gitignore:
    Ignore mercury_lib_int output files.

samples/c_interface/standalone_c/Makefile:
    chmod 0644.

samples/c_interface/.gitignore:
    Ignore object files and executables.

samples/java_interface/.gitignore:
    Ignore Java class files and executables.

samples/lazy_list/.gitignore:
samples/muz/.gitignore:
samples/rot13/.gitignore:
    Ignore executables.

samples/rot13/rot13_concise.m:
    Update call to index_det to use string.det_index.
    Added comments to clarify type inference.

samples/solutions/.gitignore:
    Ignore executables.

samples/solutions/all_solutions.m:
samples/solutions/n_solutions.m:
samples/solutions/one_solution.m:
samples/solutions/some_solutions.m:
    chmod 0644.

samples/solver_types/.gitignore:
    Ignore executables.

samples/solver_types/sudoku.m:
    Output the solution in a 3x3 grid.