1.9.2 Fix import_usearch_uc() for large files

https://github.com/joey711/phyloseq/issues/327

Error message after some wait:

Error in paste0(readLines(ucfile), collapse = "\n") :
  result would exceed 2^31-1 bytes

The updated version can read a 2.287 GB file (>19 million read-match
results) in 47 seconds without errors, with parsing into an OTU table
adding an additional 73 seconds, for 2 minutes total. This as a
single-core process on my laptop.

CHANGES IN VERSION 1.9.2
-------------------------

BUG FIXES

	- Large files cause import_usearch_uc() to have error.
		Error in paste0(readLines(ucfile), collapse = "\n") : result would
exceed 2^31-1 bytes

	- Solves Issue 327: https://github.com/joey711/phyloseq/issues/327