Fix cmake warnings, FindPASTIX/FindPTSCOTCH.

We were getting a lot of warnings due to nested `find_package` calls
within `Find***.cmake` files.  The recommended approach is to use
[`find_dependency`](https://cmake.org/cmake/help/latest/module/CMakeFindDependencyMacro.html)
in package configuration files. I made this change for all instances.

Case mismatches between `Find<Package>.cmake` and calling
`find_package(<PACKAGE>`) also lead to warnings. Fixed for
`FindPASTIX.cmake` and `FindSCOTCH.cmake`.

`FindBLASEXT.cmake` was broken due to calling `find_package_handle_standard_args(BLAS ...)`.
The package name must match, otherwise the `find_package(BLASEXT)` falsely thinks
the package wasn't found.  I changed to `BLASEXT`, but then also copied that value
to `BLAS_FOUND` for compatibility.

`FindPastix.cmake` had a typo that incorrectly added `PTSCOTCH` when looking for
the `SCOTCH` component.

`FindPTSCOTCH` incorrectly added `***-NOTFOUND` to include/library lists,
corrupting them.  This led to cmake errors down-the-line.

Fixes #2288.

cmake/FindLAPACK.cmake

@@ -26,6 +26,7 @@
 
 
 include(CheckFunctionExists)
+include(CMakeFindDependencyMacro)
 
 # This macro checks for the existence of the combination of fortran libraries
 # given by _list.  If the combination is found, this macro checks (using the
@@ -88,7 +89,7 @@ macro(check_lapack_libraries DEFINITIONS LIBRARIES _prefix _name _flags _list _b
     set(${LIBRARIES}    ${_libraries_found})
     # Some C++ linkers require the f2c library to link with Fortran libraries.
     # I do not know which ones, thus I just add the f2c library if it is available.
-    find_package( F2C QUIET )
+    find_dependency( F2C QUIET )
     if ( F2C_FOUND )
       set(${DEFINITIONS}  ${${DEFINITIONS}} ${F2C_DEFINITIONS})
       set(${LIBRARIES}    ${${LIBRARIES}} ${F2C_LIBRARIES})
@@ -135,9 +136,9 @@ endmacro()
 
 # LAPACK requires BLAS
 if(LAPACK_FIND_QUIETLY OR NOT LAPACK_FIND_REQUIRED)
-  find_package(BLAS)
+  find_dependency(BLAS)
 else()
-  find_package(BLAS REQUIRED)
+  find_dependency(BLAS REQUIRED)
 endif()
 
 if (NOT BLAS_FOUND)