fix test case expectation
bug, /df.merged/df.trimmed/g

modified:   lib/paired.Rdata.R
fix test case
add a test for the road to imputing

if it passes, then most likely the code is working okay
move load.wim.file here, and a test

so far just a test for loading the RData file from disk, not the imputed
one.  yet.

but both codes are here

also, added test files so that the test will run okay

new file:   lib/load.wim.file.R
new file:   test/data/2010/108/N/wim.agg.RData
new file:   test/data/2010/108/N/wim108N.3600.imputed.RData
new file:   test/data/2010/108/S/wim.agg.RData
new file:   test/data/2010/108/S/wim108S.3600.imputed.RData
new file:   test/test_load_wim_files.R