[Slicing] Renames option -slice-pragma into -slice-annot.

doc/slicing/user-manual-fr/slicing.tex

src/plugins/slicing/slicingCmds.ml

src/plugins/slicing/slicingParameters.ml

src/plugins/slicing/slicingParameters.mli

tests/slicing/bts0184.i

tests/slicing/bts1768.i

tests/slicing/bts179.i

tests/slicing/bts335.i

tests/slicing/bts709.c

tests/slicing/function_lvar.i

tests/slicing/keep_annot.i

tests/slicing/loops.i

tests/slicing/select_by_annot.i

tests/slicing/select_return.i

tests/slicing/sizeof.i

tests/slicing/slice_pragma_stmt.i

tests/slicing/top2.i

tests/slicing/unitialized.c

tests/sparecode/bts334.i

tests/sparecode/glob_decls.i