Use test -h instead of test -L for portability

Citing from the GNU autoconf manual:
"either form conforms to Posix 1003.1-2001, but older shells like Solaris 8
 /bin/sh support only -h"

tests/test-merge-types

@@ -1,36 +1,36 b''
 #!/bin/sh
 
 hg init
 echo a > a
 hg ci -Amadd
 
 chmod +x a
 hg ci -mexecutable
 
 hg up 0
 rm a
 ln -s symlink a
 hg ci -msymlink
 
 hg merge
 
 echo % symlink is left parent, executable is right
 
-if [ -L a ]; then
+if [ -h a ]; then
     echo a is a symlink
     readlink a
 elif [ -x a ]; then
     echo a is executable
 fi
 
 hg update -C 1
 hg merge
 
 echo % symlink is right parent, executable is left
 
-if [ -L a ]; then
+if [ -h a ]; then
     echo a is a symlink
     readlink a
 elif [ -x a ]; then
     echo a is executable
 fi