When tried to compile the document on a Windows machine using latest MiKTeX and recent versions of all LaTeX packages included in the full installation, one can notice around 150 warnings thrown because the `system.tex' file contains two lines to include the font map files of `SourceCodePro' and `opensans' using the `\pdfmapfile' command. Because the modifier `+' is used, warnings are thrown for each font map which is already included by default for the document.
IMHO it is better to use the `=' modifier, which changes the behavior a little bit: The `+' modifier reads the specified font map and ignores all duplicate font map entries (a warning is issued), while the `=' modifier reads the specified font map and replaces matching font map entries with the new entries (no warning issued). I think this is the desired behavior.
For additional information refer to the PDFTeX documentation (`pdftex-a.pdf', r655 as of November 23, 2010) on pages 24 et seq.
%
% Activate font maps
%
-\pdfmapfile{+SourceCodePro.map}
-\pdfmapfile{+opensans.map}
+\pdfmapfile{=SourceCodePro.map}
+\pdfmapfile{=opensans.map}
% Packages for fonts
%\usepackage[variablett]{lmodern}
\usepackage[scaled=.9]{sourcecodepro}