more robust way to check tesseract version

better way of checking if the tesseract version is compatible with the
script.
If the required tess version is 3.02.02, and the actual version is 3.03,
the script would have told before that the version is too old, because
303<30202, now it compares 3.03>3.0202

OCRmyPDF.sh

@@ -150,12 +150,15 @@ cd "`dirname $0`"
 ! command -v java > /dev/null && echo "Please install java. Exiting..." && exit $EXIT_MISSING_DEPENDENCY
 
 
+
 # ensure the right tesseract version is installed
 # older versions are known to produce malformed hocr output and should not be used
 reqtessversion="3.02.02"
 tessversion=`tesseract -v 2>&1 | grep "tesseract" | sed s/[^0-9.]//g`
-! [ $((`echo $tessversion | sed s/[.]//g`-`echo $reqtessversion | sed s/[.]//g`)) -ge 0 ] > /dev/null \
+tesstooold=$(echo "`echo $tessversion | sed s/[.]//2`-`echo $reqtessversion | sed s/[.]//2` < 0" | bc)
+[ "$tesstooold" -eq "1" ] \\
 	&& echo "Please install tesseract ${reqtessversion} or newer (currently installed version is ${tessversion})" && exit $EXIT_MISSING_DEPENDENCY
+
 # ensure the right GNU parallel version is installed
 # older version do not support -q flag (required to escape special characters)
 reqparallelversion="20130222"
@@ -163,11 +166,9 @@ parallelversion=`parallel --minversion 0`
 ! parallel --minversion "$reqparallelversion" > /dev/null \
 	&& echo "Please install GNU parallel ${reqparallelversion} or newer (currently installed version is ${parallelversion})" && exit $EXIT_MISSING_DEPENDENCY
 
-
 # ensure pdftoppm is provided by poppler-utils, not the older xpdf version
 ! pdftoppm -v 2>&1 | grep -q 'Poppler' && echo "Please remove xpdf and install poppler-utils. Exiting..." && $EXIT_MISSING_DEPENDENCY
 
-
 # Display the version of the tools if log level is LOG_DEBUG
 if [ $VERBOSITY -ge $LOG_DEBUG ]; then
 	echo "--------------------------------"