title: R markdown v2 to pdf. Conversion error when non-Latin characters in plots
body: <p>Non-english characters inside plots are not displayed correctly. Here is a reproducible example. </p>
  
  <pre><code>---
  title: "Untitled"
  output:
    pdf_document:
      latex_engine: xelatex
    html_document:
      highlight: tango
      theme: null
  ---
  
  This is an R Markdown document. Markdown is a simple formatting syntax for authoring HTML, PDF, and MS Word documents. For more details on using R Markdown see &lt;http://rmarkdown.rstudio.com&gt;.
  
  When you click the **Knit** button a document will be generated that includes both content as well as the output of any embedded R code chunks within the document. You can embed an R code chunk like this:
  
  ```{r}
  summary(cars)
  ```
  
  You can also embed plots, for example:
  
  ```{r, echo=FALSE}
  plot(cars, main="Τίτλος στα ελληνικά")
  ```
  </code></pre>
  
  <p>Knitting in pdf produces several lines like the following (which can be omitted of course using <code>warning = FALSE</code>) before the plot, which does not display the non-english title. </p>
  
  <pre><code>## Warning: conversion failure on 'Ξ¤ΞΟ„Ξ»ΞΟ‚ ΟƒΟ„Ξ± ΞµΞ»Ξ»Ξ·Ξ½ΞΞΞ¬' in 'mbcsToSbcs': dot substituted for &lt;ce&gt;
  ## Warning: conversion failure on 'Ξ¤ΞΟ„Ξ»ΞΟ‚ ΟƒΟ„Ξ± ΞµΞ»Ξ»Ξ·Ξ½ΞΞΞ¬' in 'mbcsToSbcs': dot substituted for &lt;a4&gt;
  ## Warning: conversion failure on 'Ξ¤ΞΟ„Ξ»ΞΟ‚ ΟƒΟ„Ξ± ΞµΞ»Ξ»Ξ·Ξ½ΞΞΞ¬' in 'mbcsToSbcs': dot substituted for &lt;ce&gt;
  ## Warning: conversion failure on 'Ξ¤ΞΟ„Ξ»ΞΟ‚ ΟƒΟ„Ξ± ΞµΞ»Ξ»Ξ·Ξ½ΞΞΞ¬' in 'mbcsToSbcs': dot substituted for
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/PGg8U.png" alt="enter image description here"></p>
  
  <p>I have found out that specifying <code>dev='cairo_pdf'</code> in the chunk options, does the trick, but then the plot is not visible in the html output.</p>
  
  <pre><code>&gt; sessionInfo()
  R version 3.1.1 (2014-07-10)
  Platform: i386-w64-mingw32/i386 (32-bit)
  
  locale:
  [1] LC_COLLATE=Greek_Greece.1253  LC_CTYPE=Greek_Greece.1253    LC_MONETARY=Greek_Greece.1253 LC_NUMERIC=C                  LC_TIME=Greek_Greece.1253    
  
  attached base packages:
   [1] datasets  grDevices splines   graphics  stats     grid      tcltk     utils     methods   base     
  
  other attached packages:
   [1] tis_1.23            GGally_0.4.7        mratios_1.3.17      fpp_0.5             lmtest_0.9-33       expsmooth_2.02      fma_2.01           
   [8] tseries_0.10-32     forecast_5.4        xts_0.9-7           stringr_0.6.2       beeswarm_0.1.6      colorspace_1.2-4    latticeExtra_0.6-26
  [15] RColorBrewer_1.0-5  amap_0.8-12         gridExtra_0.9.1     corrplot_0.73       psych_1.4.5         pgirmess_1.5.9      pastecs_1.3-18     
  [22] boot_1.3-11         xtable_1.7-3        plyr_1.8.1          zoo_1.7-11          googleVis_0.4.5     RJSONIO_1.3-0       ggthemes_1.7.0     
  [29] knitr_1.6           fBasics_3010.86     timeSeries_3010.97  timeDate_3010.98    MASS_7.3-33         RODBC_1.3-10        car_2.0-20         
  [36] sos_1.3-8           brew_1.0-6          reshape2_1.4        scales_0.2.4        ggplot2_1.0.0       svSocket_0.9-57     TinnR_1.0-5        
  [43] R2HTML_2.2.1        Hmisc_3.14-4        Formula_1.1-2       survival_2.37-7     lattice_0.20-29    
  
  loaded via a namespace (and not attached):
   [1] cluster_1.15.2   coda_0.16-1      deldir_0.1-6     digest_0.6.4     evaluate_0.5.5   formatR_0.10     fracdiff_1.4-2   gtable_0.1.2     htmltools_0.2.4 
  [10] labeling_0.2     LearnBayes_2.15  Matrix_1.1-4     munsell_0.4.2    mvtnorm_1.0-0    nlme_3.1-117     nnet_7.3-8       parallel_3.1.1   proto_0.3-10    
  [19] quadprog_1.5-5   Rcpp_0.11.2      reshape_0.8.5    rgdal_0.8-16     rmarkdown_0.2.54 sp_1.0-15        spdep_0.5-74     splancs_2.01-34  stabledist_0.6-6
  [28] svMisc_0.9-70    tools_3.1.1      yaml_2.1.13 
  </code></pre>