better error when importing a package that is not installed; xmin/xmax functions example

docs/example_generation.jl

@@ -23,8 +23,11 @@ const examples = PlotExample[
               "A simple line plot of the 3 columns.",
               [:(plot(rand(100,3)))]),
   PlotExample("Functions",
-              "Plot multiple functions",
+              "Plot multiple functions.",
               [:(plot(0:0.01:4π, [sin,cos]))]),
+  PlotExample("",
+              "You can also call it with (xmin, xmax).",
+              [:(plot([sin,cos], 0, 4π))]),
   PlotExample("Global",
               "Change the guides/background without a separate call.",
               [:(plot(rand(10); title="TITLE", xlabel="XLABEL", ylabel="YLABEL", background_color = RGB(0.5,0.5,0.5)))]),

src/plotter.jl

@@ -34,18 +34,30 @@ function plotter()
   if !(currentPackageSymbol in INITIALIZED_PACKAGES)
 
     # initialize
-    print("[Plots.jl] Initializing package: $CURRENT_PACKAGE... ")
+    println("[Plots.jl] Initializing package: $CURRENT_PACKAGE... ")
     if currentPackageSymbol == :qwt
+      try
         @eval import Qwt
+      catch
+        error("Couldn't import Qwt.  Install it with: Pkg.clone(\"https://github.com/tbreloff/Qwt.jl.git\")\n  (Note: also requires pyqt and pyqwt)")
+      end
     elseif currentPackageSymbol == :gadfly
+      try
         @eval import Gadfly
+      catch
+        error("Couldn't import Gadfly.  Install it with: Pkg.add(\"Gadfly\")")
+      end
     elseif currentPackageSymbol == :unicodeplots
+      try
         @eval import UnicodePlots
+      catch
+        error("Couldn't import UnicodePlots.  Install it with: Pkg.add(\"UnicodePlots\")")
+      end
     else
       error("Unknown plotter $currentPackageSymbol.  Choose from: $AVAILABLE_PACKAGES")
     end
     push!(INITIALIZED_PACKAGES, currentPackageSymbol)
-    println("done.")
+    println("[Plots.jl] done.")
 
   end
   CURRENT_PACKAGE.pkg