title: Error convering character value to monthly data with as.yearmon (zoo)
body: <p>Problem occurs when months' value are in the text form like "Jan" or "January".
  for example, the following line </p>
  
  <pre><code>as.yearmon("Jan-2000", "%b-%Y")
  </code></pre>
  
  <p>returns an error:</p>
  
  <pre><code>Error in charToDate(x) : &gt; character string is not in a standard unambiguous format
  </code></pre>
  
  <p>what's going wrong here?</p>
  
  <p>sessionInfo():</p>
  
  <p>R version 2.15.1 (2012-06-22)
  Platform: x86_64-pc-mingw32/x64 (64-bit)</p>
  
  <p>locale:
  [1] LC_COLLATE=Russian_Russia.1251  LC_CTYPE=Russian_Russia.1251    LC_MONETARY=Russian_Russia.1251
  [4] LC_NUMERIC=C                    LC_TIME=Russian_Russia.1251    </p>
  
  <p>attached base packages:
  [1] grid      stats     graphics  grDevices utils     datasets  methods   base     </p>
  
  <p>other attached packages:
   [1] RODBC_1.3-6         latticeExtra_0.6-24 lattice_0.20-10     gplots_2.11.0       MASS_7.3-22<br>
   [6] KernSmooth_2.23-8   caTools_1.13        bitops_1.0-4.1      gdata_2.12.0        gtools_2.7.0<br>
  [11] RColorBrewer_1.0-5  xts_0.8-6           zoo_1.7-8          </p>
  
  <p>loaded via a namespace (and not attached):
  [1] tools_2.15.1</p>