I just installe dour fasta_stats repository form the test tool shed and successfully executed your fast statistics tool, so I am not able to reproduce this behavior. There must be a configuration problem in your local Galaxy instance that is resulting in this behavior, but I cannot tell you what it is. The problem seems to be that your fasta statistics tool is not properly loaded into your Galaxy tool box, so your paster log should show an exception when attempting to load the tool after the repository is installed. Here's what my paster log shows, what does yours show?
tool_shed.util.tool_util DEBUG 2013-06-11 08:53:20,794 Loading new tool panel section: fasta
tool_shed.util.shed_util_common DEBUG 2013-06-11 08:53:20,794 Adding new row (or updating an existing row) for repository 'fasta_stats' in the tool_shed_repository table.
tool_shed.util.tool_util DEBUG 2013-06-11 08:53:20,835 Appending to tool panel section: fasta
127.0.0.1 - - [11/Jun/2013:08:53:20 -0400] "POST /admin_toolshed/prepare_for_install?includes_tools_for_display_in_tool_panel=True&encoded_repo_info_dicts=7f7b0676b166777988637e98c4b4cf254cac31b0%3A7b2266617374615f7374617473223a205b2250726f647563652062617369632073746174697374696373206f6e20612066617374612f6d756c746966617374612066696c65222c2022687474703a2f2f74657374746f6f6c736865642e67322e62782e7073752e6564752f7265706f732f73696d6f6e2d676c61646d616e2f66617374615f7374617473222c2022336563613363623739653734222c202231222c202273696d6f6e2d676c61646d616e222c207b7d2c207b7d5d7d&includes_tools=True&tool_shed_url=http%3A%2F%2Ftesttoolshed.g2.
bx.psu.edu%2F&includes_tool_dependencies=False HTTP/1.1" 200 - "
http://localhost:8763/admin_toolshed/prepare_for_install?tool_shed_url=http://testtoolshed.g2.bx.psu.edu/&repository_ids=ea3d74feddb3e781&changeset_revisions=3eca3cb79e74" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:21.0) Gecko/20100101 Firefox/21.0"
/Users/gvk/workspace/galaxy-central/lib/tool_shed/util/xml_util.py:90: FutureWarning: The behavior of this method will change in future versions. Use specific 'len(elem)' or 'elem is not None' test instead.
if elem: