Fix an error being displayed weirdly

The Debug impl was being used instead of the Display one. Also, remove the full stops from the ends of all the error messages because I’ve decided it looks weird.

src/options/misfire.rs

@@ -95,12 +95,13 @@ impl fmt::Display for Misfire {
             InvalidOptions(ref e)            => write!(f, "{}", e),
             Help(ref text)                   => write!(f, "{}", text),
             Version(ref version)             => write!(f, "{}", version),
-            Conflict(ref a, ref b)           => write!(f, "Option {} conflicts with option {}.", a, b),
-            Duplicate(ref a, ref b)          => write!(f, "Flag {:?} conflicts with flag {:?}.", a, b),
-            Useless(ref a, false, ref b)     => write!(f, "Option {} is useless without option {}.", a, b),
-            Useless(ref a, true, ref b)      => write!(f, "Option {} is useless given option {}.", a, b),
-            Useless2(ref a, ref b1, ref b2)  => write!(f, "Option {} is useless without options {} or {}.", a, b1, b2),
-            TreeAllAll                       => write!(f, "Option --tree is useless given --all --all."),
+            Conflict(ref a, ref b)           => write!(f, "Option {} conflicts with option {}", a, b),
+            Duplicate(ref a, ref b)          => if a == b { write!(f, "Flag {} was given twice", a) }
+                                                     else { write!(f, "Flag {} conflicts with flag {}", a, b) },
+            Useless(ref a, false, ref b)     => write!(f, "Option {} is useless without option {}", a, b),
+            Useless(ref a, true, ref b)      => write!(f, "Option {} is useless given option {}", a, b),
+            Useless2(ref a, ref b1, ref b2)  => write!(f, "Option {} is useless without options {} or {}", a, b1, b2),
+            TreeAllAll                       => write!(f, "Option --tree is useless given --all --all"),
             FailedParse(ref e)               => write!(f, "Failed to parse number: {}", e),
             FailedGlobPattern(ref e)         => write!(f, "Failed to parse glob pattern: {}", e),
         }

xtests/error_duplicate

@@ -0,0 +1 @@
+Flag -l conflicts with flag --long

xtests/error_twice

@@ -0,0 +1 @@
+Flag -l was given twice

xtests/error_useless

@@ -1 +1 @@
-Option --binary (-b) is useless without option --long (-l).
+Option --binary (-b) is useless without option --long (-l)

xtests/run.sh

@@ -189,6 +189,8 @@ $exa --ternary    2>&1 | diff -q - $results/error_long       || exit 1
 $exa -4           2>&1 | diff -q - $results/error_short      || exit 1
 $exa --time       2>&1 | diff -q - $results/error_value      || exit 1
 $exa --long=time  2>&1 | diff -q - $results/error_overvalued || exit 1
+$exa -l --long    2>&1 | diff -q - $results/error_duplicate  || exit 1
+$exa -ll          2>&1 | diff -q - $results/error_twice      || exit 1
 
 
 # Debug mode