patch 8.0.0167: str2nr()/str2float() fail with negative values

Problem:    str2nr() and str2float() do not always work with negative values.
Solution:   Be more flexible about handling signs. (LemonBoy, closes #1332)
            Add more tests.
diff --git a/src/testdir/test_alot.vim b/src/testdir/test_alot.vim
index 6e989f6..d29bc3a 100644
--- a/src/testdir/test_alot.vim
+++ b/src/testdir/test_alot.vim
@@ -18,6 +18,7 @@
 source test_filter_map.vim
 source test_float_func.vim
 source test_fnamemodify.vim
+source test_functions.vim
 source test_glob2regpat.vim
 source test_goto.vim
 source test_help_tagjump.vim