Fix outdated onstants names in the manual

Author: Marius Muja

doc/manual.pdf

@@ -698,9 +698,9 @@ \subsubsection{flann::Index::knnSearch}
 \begin{description}
  \item[checks] specifies the maximum leafs to visit when searching for neighbours. A
 higher value for this parameter would give better search precision, but
-also take more time. For all leafs to be checked use the value \texttt{CHECKS\_UNLIMITED}.
+also take more time. For all leafs to be checked use the value \texttt{FLANN\_CHECKS\_UNLIMITED}.
 If automatic configuration was used when the index was created, the number of checks 
-required to achieve the specified precision was also computed, to use that value specify \texttt{CHECKS\_AUTOTUNED}.
+required to achieve the specified precision was also computed, to use that value specify \texttt{FLANN\_CHECKS\_AUTOTUNED}.
  \item[eps] Search for eps-approximate neighbors (only used by KDTreeSingleIndex and KDTreeCuda3dIndex).
  \item[sorted] Used only by radius search, specifies if the neighbors returned should be sorted by distance.
  \item[max\_neighbours] Specifies the maximum number of neighbors radius search should return (default: -1 =