Make sure we start off with null() temp vstrings

See issue #31. This should avoid the reported crash,
but the tests I've tried don't trip the segfault.
But anyway, add two tests for sax with double
parsing.

sax/m_sax_parser.F90

@@ -396,6 +396,7 @@ end subroutine startEntity_handler
     nullURI => null()
 #endif
     tempString => null()
+    tempString2 => null()
     elem => null()
     attDecl => null()
 

sax/test/test_sax_parser_4.f90

@@ -0,0 +1,24 @@
+program test_sax_reader
+
+  use FoX_sax
+  type(xml_t) :: xp
+  integer :: iostat
+
+  ! Can we parse the same file twice?
+
+  call open_xml_file(xp, "test_sax_fsm_1.in", iostat)
+
+  write(*,'(i1)') iostat
+
+  call parse(xp)
+
+  call close_xml_t(xp) 
+
+  call open_xml_file(xp, "test_sax_fsm_1.in", iostat)
+
+  write(*,'(i1)') iostat
+
+  call parse(xp)
+
+  call close_xml_t(xp) 
+end program test_sax_reader

sax/test/test_sax_parser_4.out

@@ -0,0 +1,2 @@
+0
+0

sax/test/test_sax_parser_5.f90

@@ -0,0 +1,18 @@
+program test_sax_reader
+
+  use FoX_sax
+  type(xml_t) :: xp
+  integer :: iostat
+
+  ! Can we parse the same file twice?
+
+  call open_xml_file(xp, "testin.xml", iostat)
+
+  write(*,'(i1)') iostat
+
+  call parse(xp)
+
+  call parse(xp)
+
+  call close_xml_t(xp) 
+end program test_sax_reader

sax/test/test_sax_parser_5.out

@@ -0,0 +1 @@
+0