don't pass LDFLAGS when only performing compilation (-c)

This simplifies the compiler commands and suppresses warnings.
Merge pull request #123 from longjon/master

don't pass LDFLAGS when only performing compilation (-c)
fix detector's coordinate mapping for images smaller than IMAGE_DIM
Properly index windows in detector list mode

Fix iteration over single windows: whether one or more windows are
listed for an image, generate windows as a list.
add SplitLayer and Net::AddSplits to transform shared bottom blobs into
split layers
make split_layer backward obey propagate_down
add split layer tests
add split layer tests
add split layer insertion tests; move split insertion code to util file
some cleanup
Merge pull request #116 from aravindhm/tanh

Add TanH = hyperbolic tangent activation layer (popular for sparse
autoencoders).
eliminate redundant code with get_split_blob_name method
change \n's to less distracting spaces in hard-coded proto strings
give first top split blob same name as bottom blob
allow in place computation of SplitLayer 0th top blob
change \" in test_split_layer to ' for readability
remove pointlessly duplicated CheckGradientExhaustive calls (I screwed
up when merging, I think)
fix comment typo
add test for layer with two tops that are inputs to multiple layers
remove redundant add_bottom (immediately cleared and then re-added)