Add more verbose progress reporting to forward_index creation.
Add more verbose progress reporting to forward_index creation.

This is particularly useful when indexing really large libsvm-formatted
corpora.

gef756/meta,husseinhazimeh/meta,husseinhazimeh/meta,esparza83/meta,saq7/MeTA,saq7/MeTA,gef756/meta,husseinhazimeh/meta,esparza83/meta,esparza83/meta,husseinhazimeh/meta,saq7/MeTA,esparza83/meta,husseinhazimeh/meta,gef756/meta,esparza83/meta,gef756/meta,gef756/meta