for R <= 3.2.2, Unicode chars don't work for shiny mainly because we want to
preserve the source reference, and unfortunately srcfilecopy() fails because of
the bug https://bugs.r-project.org/bugzilla3/show_bug.cgi?id=16264
here I use lines = '' to get around the bug, and assign the source lines to
the srcfile object later, so there is no grep("\n", multibyte_chars) occuring
I also replaced source() with a custom version, which is much simpler and works
better with Unicode chars
89fe2ff217